Patent Publication Number: US-10783147-B2

Title: Query result flow control in a network switch

Description:
BACKGROUND 
     Computing devices may store information in memory. In a network environment, multiple computing devices may interact as components of a system. Sometimes computing devices in a first location need to access information stored in the memory of a second computing device in a second location. Similarly, computing devices in a first location may need to write information to the memory of a second computing device. 
     SUMMARY 
     In one aspect, a network device in accordance with embodiments of the invention includes a standing query instance (SQI) and a database. The SQI is programmed to generate an output stored in a low resource storage table of a database. The database is programmed to monitor a storage capacity of the low resource storage table based on at least, in part, the output stored in the low resource storage table; determine, based on the monitoring, when the storage capacity reaches a predetermined amount; and disable an upstream element in response to the determination. 
     In one aspect, a method of operating a network device in accordance with embodiments of the invention includes obtaining, by a database of the network device, an output generated by a standing query instance (SQI); storing, by the database, the output in a low resource storage table of the database in response to obtaining the output; making a first determination, by the database, that a storage capacity of the low resource storage table has reached a predetermined amount; and preventing, by the database, the SQI from generating a second output, to be stored in the low resource storage table, in response to the first determination. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Certain embodiments of the invention will be described with reference to the accompanying drawings. However, the accompanying drawings illustrate only certain aspects or implementations of the invention by way of example and are not meant to limit the scope of the claims. 
         FIG. 1A  shows a diagram of a system in accordance with one or more embodiments of the invention. 
         FIG. 1B  shows a diagram of a network device in accordance with one or more embodiments of the invention. 
         FIG. 2  shows a database in accordance with one or more embodiments of the invention. 
         FIG. 3  shows a diagram of a database distributed across multiple network devices in accordance with one or more embodiments of the invention. 
         FIG. 4  shows a diagram of a database distributed across multiple processes in accordance with one or more embodiments of the invention. 
         FIG. 5  shows a table of a database in accordance with one or more embodiments of the invention. 
         FIG. 6A  shows a diagram of a standing query instance including a materialized output in accordance with one or more embodiments of the invention. 
         FIG. 6B  shows a diagram of a standing query instance including a non-materialized output in accordance with one or more embodiments of the invention. 
         FIG. 7A  shows a diagram of a standing query including a materialized output interacting with a database in accordance with one or more embodiments of the invention. 
         FIG. 7B  shows a diagram of a standing query including a non-materialized output interacting with a database in accordance with one or more embodiments of the invention. 
         FIG. 8A  shows a flowchart of a method of generating a standing query instance in accordance with one or more embodiments of the invention. 
         FIG. 8B  shows a flowchart of a method of operating a database in accordance with one or more embodiments of the invention. 
         FIG. 8C  shows a flowchart of a method of generating observers in accordance with one or more embodiments of the invention. 
         FIG. 8D  shows a flowchart of a method of generating modifiers in accordance with one or more embodiments of the invention. 
         FIG. 8E  shows a flowchart of a second method of generating observers in accordance with one or more embodiments of the invention. 
         FIG. 8F  shows a flowchart of a second method of generating modifiers in accordance with one or more embodiments of the invention. 
         FIG. 9A  shows a flowchart of a method of obtaining modifications to a table in accordance with one or more embodiments of the invention. 
         FIG. 9B  shows a flowchart of a method of evaluating a standing query instance (SQI) in accordance with one or more embodiments of the invention. 
         FIG. 9C  shows a flowchart of a method of propagating output to a table in accordance with one or more embodiments of the invention. 
         FIG. 10  shows a flowchart of a method of managing temporary storage in accordance with one or more embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Specific embodiments will now be described with reference to the accompanying figures. In the following description, numerous details are set forth as examples of the invention. It will be understood by those skilled in the art that one or more embodiments of the present invention may be practiced without these specific details and that numerous variations or modifications may be possible without departing from the scope of the invention. Certain details known to those of ordinary skill in the art are omitted to avoid obscuring the description. 
     In general, embodiments of the invention relate to methods and systems for storing and/or accessing information stored in one or more network devices. Each of the network devices may be a router, switch, multilayer switch, or other device that may support network communications or may interact with other devices through the network. 
     The stored information may relate to a state of the network device, a state of a network to which a network device is connected, and/or a state of one or more services operating on a network device. For example, the stored information may be a temperature of a component of the network device. The component may be, for example, a processor. In another example, the stored information may be an accessibility of another network device. The stored information may be other information without departing from the invention. 
     A network device in accordance with one or more embodiments of the invention may include a database. The database may include tables that store information. In one or more embodiments of the invention, the database may span across multiple network devices, e.g., portions of the database may be stored on storage of a first network device and other portions of the database may be stored on storage of a second network device. In one or more embodiments of the invention, duplicate copies of information stored in the database may be stored on the first network device and the second network device. In one or more embodiments of the invention, a database planner may manage the consistency of the database across one or more network devices, e.g., may make copies of information stored on a first network device. 
     The network device may include a standing query service (SQS) manager. The SQS manager may generate and/or manage instances of SQSs that operate on information stored in the database. Instances of SQS may be generated in response to requests from other entities. In one or more embodiments of the invention, the other entities may be agents executing on the network device or agents executing on other network devices. 
     Each instance of a SQS may include an input table, a query, and may generate an output. An instance of the SQS may operate on entries of the input table to produce the output. In one or more embodiments of the invention, the instance of the SQS may generate an output in response to a change in an input table of the instance of the SQS. In one or more embodiments of the invention, the instance of the SQS may generate an output after one or more predetermined changes to the input table have occurred. In one or more embodiments of the invention, the instance of the SQS may produce an output at a predetermined time, e.g., periodically or at one or more predetermined times. 
     The entries of input tables of an instance of a SQS may be generated by observers. Observers may monitor entries of the database and/or output tables of other instances of SQSs and propagate changes to the database and/or output tables to input tables associated with the observer. In one or more embodiments of the invention, observers may also propagate changes to entries of the database to one or more agents of the network device. 
     In one or more embodiments of the invention, the output produced by the query of a standing query instance (SQI) may be propagated to an output table by a modifier. Modifiers may monitor queries of instances of SQS and propagate the output of the queries to output tables in response to changes in the output of the query. In one or more embodiments of the invention, the output table may be a portion of the database, e.g., a table of the database or entries of a table of the database. 
     In one or more embodiments of the invention, the output produced by the query of a SQI may be propagated to a temporary storage rather than an output table by a modifier. The temporary storage may be, for example, a table of the database that is not presented to agents, queries, or other entities. A table that is not presented to agents, queries, or other entities may be a non-materialized table. As output is read from the table, the output may be deleted from the table. A non-materialized table may be a low resource storage table that utilizes fewer computational resources of the network device than a materialized table. 
     In one or more embodiments of the invention, a non-materialized table may have a finite, predetermined storage capacity. When output that is stored in the non-materialized table at a rate faster than a rate at which output is read from the non-materialized table and subsequently deleted, the utilized storage capacity of the non-materialized table may approach and/or reach the predetermined storage capacity of the non-materialized table. When the utilized storage capacity approaches and/or reaches the predetermine storage capacity of the non-materialized table, the database may be programmed to decrease the rate at which output is stored in the non-materialized table and/or increase the rate at which output is read from the non-materialized table. 
     In one or more embodiments of the invention, the database decreases the rate at which output is stored in the non-materialized table by suspending execution of an upstream entity. In one or more embodiments of the invention, the upstream entity is a SQI and/or compiled query of a SQI that generates output stored in the non-materialized table. In one or more embodiments of the invention, the upstream entity is an observer that triggers a SQI and/or compiled query of a SQI to generate output that is stored in the non-materialized table. 
     In one or more embodiments of the invention, the database increases the rate at which output is read from the non-materialized table by signaling a downstream entity to increase a read rate. In one or more embodiments of the invention, the downstream entity is an observer. In one or more embodiments of the invention, the downstream entity is an agent. In one or more embodiments of the invention, the downstream entity is a SQI. 
       FIG. 1A  shows an example of a network in accordance with one or more embodiments of the invention. The example network shown in  FIG. 1  includes network devices ( 10 A- 10 N) operably connected to one another. Each of the aforementioned network devices may be interconnected by a network ( 40 ) supporting one or more networking protocols. For example, network device  10 A may be connected by operable communication links to network devices  10 M,  20 A, and  20 N as indicated by the arrows. The network ( 40 ) may include any number of network devices without departing from the invention. Additionally, each of the aforementioned network devices may include any number of communication links without departing from the invention. In one embodiment of the invention, the network ( 40 ) may be the Internet. In another embodiment of the invention, the network ( 40 ) may be an intranet. The intranet may be connected to the Internet. 
       FIG. 1B  shows a network device ( 100 ) in accordance with one or more embodiments of the invention. The network device ( 100 ) may be configured to store information in a database ( 120 ) and generate outputs based on the information stored in the database ( 120 ) by one or more instances of SQSs. The generated output may be materialized, e.g., stored in accessible tables of the database, or non-materialized, e.g., stored in non-accessible tables of the database and deleted from the non-accessible tables as the output is received by entities that requested the creation of the output. 
     The network device ( 100 ) may be a physical device that includes non-transitory storage, memory (e.g. Random Access Memory), and one or more processors. The non-transitory storage may include instructions which, when executed by the one or more processors, enable the network device ( 100 ) to perform the functions described in this application and shown in  FIGS. 8A-10 . 
     The network device ( 100 ) may include a SQS manager ( 110 ), one or more standing query services ( 111 A- 111 M), a database ( 120 ), and a one or more agents ( 130 ). The network device ( 100 ) may be operably connected to one or more entities ( 140 ). The entities ( 140 ) may be, for example, other network devices, servers, or computing devices accessible by a network. Each of the components of the network device ( 100 ) is described below. 
     The network device ( 100 ) may include a database ( 120 ). The database ( 120 ) may be a managed storage database that controls read and/or write access to information stored in the database. Read access to the database ( 120 ) may be provided by one or more observers and write access to the database may be provided by one or more modifiers. Observers and modifiers may be dynamically generated and removed. Observers and modifiers may be registered with the database ( 120 ) and thereby notify the database ( 120 ) of their presence. The interaction of observers and modifiers with the database are described in greater detail with respect to  FIGS. 6A-7B . 
     In one or more embodiments of the invention, the database ( 120 ) may include one more tables ( 200 A- 200 N) as shown in  FIG. 2 . The tables ( 200 A- 200 N) may be data structures for storing information on a computer readable storage medium of the network device ( 100 ). Each element of each table may include one or more information elements. Information elements may be, for example, integers, characters, floating point values, addresses, or any other type of data. 
       FIG. 5  shows an example of Table A ( 200 A) in accordance with one or more embodiments of the invention. Table A ( 200 A) includes a number of information elements ( 500 ,  510 ). As discussed above, each information element may include data of varying type. 
     In one or more embodiments of the invention, the database ( 120 ) may include a write history associated with each information element of each table of the database ( 120 ). The write history of an information element of a table may include a list of modifications, e.g., writes, to the element and the time of each modification. The list of modifications may include all of the modifications or a portion of the modifications. For example, information element A ( 500 ) may have an associated element A write history ( 505 ) that includes one or more modifications that have been made in a sequence to information element A ( 500 ). While the element A write history ( 505 ) is shown as being a part of Table A ( 200 A) in  FIG. 5 , the write history of each information element of each table may be stored in other locations without departing from the invention. 
     In one or more embodiments of the invention, the database ( 120 ) may include a subscription list ( 506 ) associated with each information element of each table of the database ( 120 ). The subscription list ( 506 ) associated with each element may be a list of observers and/or modifiers, registered with the database, that interact with the associated information element. When an information element is updated, e.g., written to an information element by a modifier, the database may notify each entity listed in the subscription list ( 506 ) associated with the information element that the information element was updated. 
     In one or more embodiments of the invention, each subscription list associated with each information element of the database ( 120 ) may include a history list position of each observer. Observers may read information from the database at predetermined times, periodically, and/or in real-time in response to notifications of updates to information from the database ( 120 ). When an observer requests to read information from an information element of the database ( 120 ), the database ( 120 ) may return one or more modifications listed in the write history list, associated with the information element, having a write time that is later than a write time of the history list position. By sending one or more of the modifications having a write time that is later than the write time of the history list position, information written to the information element may be provided to the observer and thereby propagated to any requesting entities. The database ( 120 ) may update the history list position of the observer as the observer reads modifications from the history list. 
     In one or more embodiments of the invention, when an observer requests to read information from an information element of the database ( 120 ), the database ( 120 ) may continue to return modifications until the history list position of the observer is updated to the most recent modification. 
     In an example, information element A ( 500 ) may have an associated element A subscription list ( 506 ) and information element N ( 510 ) may have an associated element N subscription list ( 516 ). Each of the subscription lists ( 506 ,  516 ) may include a listing of observers that are observing information elements A ( 500 ) and N ( 510 ), respectively. Each of the subscription lists ( 506 ,  516 ) may also include the history list position of each observer with respect to element A write history ( 505 ) and element N write history ( 515 ). The history list position of each observer with respect to each write history may be different, e.g., a first observer may have a history list position that is at a later time than a history list position of a second observer that is observing the same information element as the first observer. Thus, each information element may have a different subscription list and each entity listed in the subscription list may have a different history list location. 
     In one or more embodiments of the invention, the database ( 120 ) may remove elements of a write history of an information element when all of the entities subscribed to the information element have read the element. Removing the elements of the write history that have been read by all subscribed entities may reduce the storage requirements of the database. 
     While the element A subscription list ( 506 ) and element N subscription list ( 516 ) are shown as being a part of Table A ( 200 A) in  FIG. 5 , the subscription list associated with each information element of each table may be stored in other locations without departing from the invention. 
     In one or more embodiments of the invention, tables of the database may be materialized or non-materialized, e.g., used as temporary storage ( 205 ,  FIG. 2 ). Materialized tables of the database may be accessible and/or viewable by other entities. Non-materialized tables may not be accessible and/or viewable by other entities. 
     In one or more embodiments of the invention, the database may delete entries of the non-materialized tables when the entries have been consumed, e.g., read or otherwise propagated to subscribed entities. As discussed above, each information element of a table may have an associated write history and subscription list. The write history and subscription list may indicate that other entities intend to consume, e.g., receive the data stored in the information element, the information element. When the write history and subscription list indicate that all entities have consumed the associated information element, the information element may be deleted. 
     Returning to  FIG. 2 , the database ( 120 ) may include tables ( 200 A- 200 N) that are located on multiple network devices and/or are stored in multiple address spaces.  FIGS. 3 and 4  illustrate examples of tables distributed across multiple devices and/or multiple address spaces. 
     In one or more embodiments of the invention, the database ( 120 ) may span across multiple network devices as shown in  FIG. 3 .  FIG. 3  shows an example of a database ( 120 ) spanning across multiple network devices ( 300 ,  310 ,  320 ) connected by a network ( 40 ) in accordance with embodiments of the invention. The database ( 120 ) spans across each of the network devices and includes tables ( 300 A,  300 B, and  300 C) stored on a computer readable storage medium of each network device, respectively. For example, Table A ( 300 A) may be stored on a computer readable storage medium of network device A ( 300 ), Table B ( 300 B) may be stored on a computer readable storage medium of network device B ( 310 ), and/or Table C ( 300 C) may be stored on a computer readable storage medium of network device C ( 320 ). Each of the tables ( 300 A,  300 B,  300 C) may include the same information, e.g., duplicate, or different information, e.g., non-duplicative. In some embodiments, each of the tables ( 300 A,  300 B,  300 C) may include duplicate and non-duplicate information. 
     For example, each of the tables ( 300 A,  300 B,  300 C) may include a first entry that comprises the maximum data transmission speed of the network ( 40 ). Table A ( 300 A) may also include a second entry, not present in either Table B ( 300 B) or Table C ( 300 C), that comprises the current temperature of a processor of network device A ( 300 ). 
     In one or more embodiments of the invention, the database ( 120 ) may span across multiple processes in separate address spaces executing on a single network device.  FIG. 4  shows an example of a database ( 120 ) spanning across a first process ( 410 ) and a second process ( 420 ) of a network device ( 400 ) in accordance with embodiments of the invention. The database ( 120 ) spans across each of the processes ( 410 ,  420 ) and includes tables ( 430 A,  430 B) stored on a computer readable storage medium of the network device ( 400 ). Table A ( 430 A) and Table B ( 430 B) may be stored in different address spaces allocated to the first process ( 410 ) and the second process ( 420 ), respectively. Each of the tables ( 430 A,  430 B) may include the same information, e.g., duplicate, or different information, e.g., non-duplicative. In some embodiments, each of the tables ( 430 A,  430 B) may include duplicate and non-duplicate information. 
     For example, each of the tables ( 430 A,  430 B) may include a first entry that comprises a maximum inter-process memory transport rate of the network device ( 400 ). Table A ( 430 A) may also include a second entry, not present in Table B ( 430 B), that comprises the quantity of storage allocated to the first process ( 410 ). 
     Returning to  FIG. 2 , the network device may include a database planner ( 210 ). The database planner ( 210 ) may manage the database ( 120 ). Managing the database ( 120 ) may comprise maintaining the location of each table of the database and facilitating inter network device and/or inter process memory transfers between tables of the database. For example, an agent present on a first network device may request to read data from a table that is present on a second network device. In response to the request from the agent, the database planner ( 210 ) may provide the location of the table on the second network device and thereby enable the agent to retrieve the data from the second table. In one or more embodiments of the invention, the database planner ( 210 ) may generate an observer, in response to requests from entities. The generated observer may retrieve data from a table of the database and provide the data to the requesting entity as describe with respect to  FIG. 5 . In some embodiments of the invention, managing the database ( 120 ) may comprise maintaining the location of each table of the database across shared memory. 
     In one or more embodiments of the invention, the database planner ( 210 ) may include a data structure, e.g., a list, tree, or other structure, that includes the location of each unique entry of the database ( 120 ). A unique entry may be an entry of a table where information is first written into the database ( 210 ). The information may be subsequently written to other entries of other tables of the database as duplicative information. The data structure may include the information necessary to determine the location of each unique entry of the database ( 120 ) and thereby enable data included in any entry of the database ( 120 ) to be retrieved and or duplicated to other tables of the database ( 120 ). In one or more embodiments of the invention, the database ( 120 ) may present requesting entities with information relating to materialized entries of the database. In one or more embodiments of the invention, the database ( 120 ) may not present requesting entities with information relating to non-materialized entries of the database. 
     In one or more embodiments of the invention, the database planner ( 210 ) may be executing on the network device and include functionality to update each table of the database ( 120 ) in response to a change in an entry of the database. For example, the database planner ( 210 ) may include functionality to identify changes to entries of a first table of the database and propagate those changes to the other tables of the database by writing duplicative information to each of the other tables. In one or more embodiments of the invention, the database planner ( 210 ) may include functionality to monitor entries of a first table and notify other tables of changes to the entries of the first table. In response to the notification, the other tables may note that the entries of the first table have changed and may thereby notify, in response to requests from agents or other entities, the agents or other entities that entries of the first table have changed. 
     Thus, the database planner ( 210 ) may enable the database ( 120 ) to provide information to an agent or other entity of the location of any entry of any table of the database ( 120 ). 
     Returning to  FIG. 1B , in one or more embodiments of the invention, the SQS manager ( 110 ) may include functionality to manage SQSs. The SQS manager ( 110 ) may manage one or more SQSs ( 111 A- 111 M). 
     Managing SQSs may include generating instances of SQSs in response to requests from agents ( 130 ), generating observers associated with instances of the SQSs ( 111 A- 111 M), and/or generating modifiers associated with the instances of the SQSs ( 111 A- 111 M). The SQS manager ( 110 ) may generate instances of SQSs ( 111 A- 111 M), observers, and modifiers based on information stored in or derived from the database ( 120 ) and/or a database planner ( 210 ,  FIG. 2 ). Instances of SQSs may include an output that is materialized or non-materialized. Methods of managing the instances of the SQSs are further described with respect to  FIGS. 8A and 8C-8E  and SQSs are further described with respect to  FIGS. 6A-7B . 
     In one or more embodiments of the invention, the SQS manager ( 110 ) may be an embedded hardware device. The embedded hardware device may be, for example, a field programmable gate array (FPGA), application specific integrated circuit (ASIC), and/or digital signal processor (DSP). Other embedded hardware devices may be used without departing from the invention. In one or more embodiments of the invention, the embedded hardware device may be a component of an external entity ( 140 ) and provide the functionality by remotely communicating with the network device ( 100 ) by a network. 
     In one or more embodiments, the SQS manager ( 110 ) may comprise instructions, stored on a non-transitory computer readable storage medium, that when executing on a processor of the network device ( 100 ) cause the network device ( 100 ) to perform the functionality of the SQS manager ( 110 ). In one or more embodiments of the invention, the SQS manager ( 110 ) may be executed by processors of external entities ( 140 ) and cause the network device ( 100 ) to perform the functionality of the SQS manager ( 110 ) by remotely communicating with the network device ( 100 ) by an operable connection. 
     Each of the SQSs ( 111 A- 111 M) may include one or more instances of a standing query. An example of a QI ( 600 ) including a materialized output in accordance with one or more embodiments of the invention is shown in  FIG. 6A . The QI ( 600 ) includes a compiled query ( 610 ) and one or more constraint parameters ( 615 ). Each of the components of the example QI ( 600 ) is described below. 
     The QI ( 600 ) may include a compiled query ( 610 ). The compiled query ( 610 ) may include instructions that, when executed by a processor, generate an output based on information included in an input table(s) ( 620 ) associated with the QI ( 600 ) and constraint parameters ( 615 ) of the QI ( 600 ). In one or more embodiments of the invention, the compiled query ( 610 ) may generate output in response to a change in value of one or more entries of the input table(s) ( 620 ). In one or more embodiments of the invention, the compiled query ( 610 ) may generate output at predetermined times. In one or more embodiments of the invention, the predetermined times may be periodic, e.g., the compiled query ( 610 ) may generate an output every five seconds. 
     The constraint parameters ( 615 ) may modify the manner in which the compiled query ( 610 ) generates an output, e.g., scales output, excludes input used to determined output, modifies weight of an input, etc. 
     The input table ( 620 )( s ) may be a data structure including one or more elements. The elements of the input table ( 620 )( s ) may be generated by one or more observers, as will be discussed in greater detail with respect to  FIG. 7A . 
     Output generated by the compiled query ( 610 ) may be sent to a modifier ( 650 ) associated with the QI ( 600 ). The modifier ( 650 ) may propagate the output of the SQI ( 610 ) to the output table ( 630 ) associated with the QI ( 600 ). The output table ( 630 ) will be discussed in greater detail with respect to  FIG. 7A . 
     An example of a QI ( 600 ) including a non-materialized output in accordance with one or more embodiments of the invention is shown in  FIG. 6B . A SQI that includes a non-materialized output may store its output in a temporary storage ( 660 ) rather than an out table ( 630 ,  FIG. 6A ). 
     Returning to  FIG. 1B , the network device ( 100 ) may include one or more agents ( 130 ) executing on the network device ( 100 ) in accordance with one or more embodiments of the invention. The agents ( 130 ) may interact with the database ( 120 ) of the network device ( 100 ), e.g., the agents may desire to read and/or write data to and/or from the database ( 120 ). For example, the agents ( 130 ) may generate data to be stored in the database ( 120 ) or may need to read information from the database ( 120 ). In response to read or write requests from the agents ( 130 ), the database ( 120 ) and/or the database planner ( 210 ,  FIG. 2 ) may generate observers or modifiers as required to facilitate the transfer of information between the database ( 120 ) and the agents ( 130 ). 
     The agents ( 130 ) may also interact with the SQS manager ( 110 ) of the network device ( 100 ). In an example, an agent ( 130 ) may determine information derived from information stored in the database ( 120 ). To determine the information, the agent ( 130 ) may send a request for a new SQI to the SQS manager ( 110 ) to determine the derived information. The SQS manager ( 110 ) may generate a new SQI in response to the request and one or more observers to propagate information generated by the new SQI to the agent ( 130 ). The SQI may be generated with a materialized or non-materialized output, as described above. In one or more embodiments of the invention, the SQI may be generated with a materialized or a non-materialized output based on, at least in part, information included in the new SQI request. 
       FIG. 7A  shows the example of the query instance (SI) ( 600 ) including a materialized output, shown in  FIG. 6A , interacting with a database ( 120 ) in accordance with one or more embodiments of the invention. In the example shown in  FIG. 7A , the QI ( 600 ), observers ( 700 ,  701 ), and modifier ( 710 ) were generated in response to a request from an agent ( 720 ). The request included a query type to be generated, constraint parameters, and a list of one or more information elements of the database ( 120 ) to be used as input to the compiled query ( 610 ). 
     A first observer ( 700 ) was generated to read information from the database ( 120 ) and supply the information to the compiled query ( 610 ) via an input table. More specifically, the first observer ( 700 ) observes information elements stored in one or more tables ( 200 A- 200 N) of the database and propagates the information to the compiled query ( 610 ). 
     A second observer ( 701 ) was generated to read output, generated by the compiled query ( 610 ), stored in the output table ( 630 ) associated with the QI ( 600 ) and supply the output to the agent ( 720 ) requested the QI ( 600 ). 
     A modifier ( 710 ) was generated to propagate output generated by the compiled query ( 610 ) to the output table ( 630 ). While the output table ( 630 ) is shown as a separate table in  FIG. 7A , the output table ( 630 ) may be a portion of any table of the database ( 120 ) without departing from the invention. 
     Thus, as shown in  FIG. 7A , SQIs interacting with the database ( 120 ) read and write information to or from the database by observers and modifiers, respectively. Similarly, agents interacting with the database ( 120 ) also read and write information to or from the database by observers and modifiers. 
       FIG. 7B  shows the example of a QI ( 600 ) including a non-materialized output stored in a temporary storage ( 660 ), shown in  FIG. 6B , interacting with a database ( 120 ) in accordance with one or more embodiments of the invention. In the example shown in  FIG. 7B , the QI ( 600 ), observers ( 700 ,  701 ), and modifier ( 710 ) were generated in response to a request from an agent ( 720 ). The request included a query type to be generated, constraint parameters, and a list of one or more information elements of the database ( 120 ) to be used as input to the compiled query ( 610 ). 
     A first observer ( 700 ) was generated to read information from the database ( 120 ) and supply the information to the compiled query ( 610 ) via an input table. More specifically, the first observer ( 700 ) observes information elements stored in one or more tables ( 200 A- 200 N) of the database and propagates the information to the compiled query ( 610 ). 
     A second observer ( 701 ) was generated to read output, generated by the compiled query ( 610 ), stored in the temporary storage ( 660 ) associated with the QI ( 600 ) and supply the output to the agent ( 720 ) that requested the QI ( 600 ). 
     A modifier ( 710 ) was generated to propagate output generated by the compiled query ( 610 ) to the temporary storage ( 660 ), in contrast to the output table as shown in  FIG. 7B . While the temporary storage ( 660 ) is shown as a separate table in  FIG. 7B , the temporary storage ( 660 ) may be a portion of any table of the database ( 120 ) without departing from the invention. 
     As discussed above, unlike a materialized output stored in a table that of the database ( 120 ) that may have a dynamically adjustable storage capacity to accommodate any quantity of output, a non-materialized output has a finite, predetermined storage capacity. As output is generated by the compiled query ( 610 ) and stored in the temporary storage ( 660 ), the temporary storage ( 660 ) may become full, e.g., the available storage capacity of the temporary storage ( 660 ) may approach and/or reach the maximum storage capacity of the temporary storage ( 660 ). 
     In one or more embodiments of the invention, the database ( 120 ) may be programmed to prevent the temporary storage ( 660 ) from exceeding its maximum storage capacity. In one or more embodiments of the invention, the database ( 120 ) may reduce a rate of output generation that is stored in the temporary storage ( 660 ) to prevent the temporary storage ( 660 ) from exceeding its maximum storage capacity. In one or more embodiments of the invention, the database ( 120 ) may increase a read rate of a consumer of the output stored in the temporary storage ( 660 ) to prevent the temporary storage ( 660 ) from exceeding its maximum storage capacity. Methods of operating a database to prevent exceeding the storage capacity of temporary storage, e.g., non-materialized tables, are further described with respect to  FIG. 8B . 
     Thus, as shown in  FIGS. 7A and 7B , SQIs may store output in a materialized or a non-materialized table of the database ( 120 ). 
       FIG. 8A  shows a flowchart in accordance with one or more embodiments of the invention. The method depicted in  FIG. 8A  may be used to generate SQIs in response to requests from entities such as, for example, agents in accordance with one or more embodiments of the invention. One or more steps shown in  FIG. 8A  may be omitted, repeated, and/or performed in a different order among different embodiments. 
     In Step  800 , a SQS manager of a network device obtains a request for a new instance of a SQS. The SQS manager may obtain the request from a message from an agent. The agent may be executing on the network device on which the SQS manager is executing. The request may include a query type, one or more constraint parameters, and information stored in a database on which the new instance of the SQS is to operate. 
     In Step  801 , the SQS manager determines whether a SQS matching the query type included in the request exists on the network device. If the query type does not match an existing SQS, the method proceeds to Step  804 . If the query type does match an existing SQS, the method proceeds to Step  806 . 
     In Step  802 , the SQS manager generates a new SQS based on the obtained query request. Specifically, the SQS manager may generate a new SQS including the query type indicated in the obtained query request. 
     In one or more embodiments of the invention, generating a new SQS may include compiling a query. In one or more embodiments of the invention, generating a new SQS may include linking compiled byte code. 
     In Step  803 , the SQS manager determines whether the constraint parameters of an instance of a SQS matches the constraint parameters, included in the obtained request, exists on the network device. If the constraint parameters of the obtained request do not match the constraint parameters of an existing instance of a SQS, the method proceeds to Step  808 . If the constraint parameters of the obtained request do match the constraint parameters of an existing instance of a QS, the method proceeds to Step  86 . 
     In Step  804 , the SQS manager generates a new SQI of the SQS, corresponding to the query type included in the obtained request, including constraint parameters based on the constraint parameters included in the obtained request. Specifically, the SQS manager may make a copy the compiled query associated with the SQS corresponding to the query type included in the obtained request and constrain the compiled query based on the constraint parameters included in the obtained request. 
     In one or more embodiments of the invention, the constraint parameters change the behavior of the compiled query. The constraint parameters may be variables, utilized by the compiled query, which change the output produced by the compiled query when operating on the same input. 
     In Step  805 , the SQS manager generates observers and/or modifiers associated with the new SQI. The SQS manager may generate one or more observers associated with the new SQI that supplies the compiled query of the new SQI with data on which the compiled query operates. The observers may supply the data to an input table of the new SQI as shown, for example, in  FIGS. 7A and 7B . The SQS manager may also generate one or more modifiers associated with the SQI that propagates output generated by the compiled query of the SQI. The modifiers may propagate the output generated by the compiled query to an output table associated with the new SQI. 
     In one or more embodiments of the invention, the SQS manager may generate one or more observers associated with an agent from which the request was obtained in Step  800 . The observer may be linked with the output table where data generated by the compiled query is stored and the agent from which the request was obtained in Step  800 . The observer may propagate changes to the output table to the agent and thereby notify the agent of new output generated by the new instance of the SQI requested by the agent. 
     Returning to Step  803 , the method may proceed to Step  806  if an existing SQI includes constraint parameters that are the same as those included in the SQ request obtained in Step  800 . 
     In Step  806 , the SQS manager generates observer(s) associated with an agent from which the new SQI request was obtained in Step  800 . The observer may be linked with the output table where data generated by the existing SQI identified in Step  806  is stored and the agent from which the request was obtained in Step  800 . The observer may propagate changes to the output table to the agent and thereby notify the agent of new output generated by the existing instance of the SQS. In other words, if an existing SQI includes the same constrain parameters as those of the request, an observer may be generated to propagate results of the existing SQI to the agent rather than generating a new SQI and a new modifier. 
     In one or more embodiments of the invention, the observer may propagate changes to the output table to an agent in response to a notification from the database that the element of the database the observer is observing, e.g., one or more elements of the output table, have changed. 
     In one or more embodiments of the invention, the observer may poll the database at predetermined times to determine if the observed elements of the database have changed. If the database indicates the observed elements of the database have changed, the observer may receive each modification to the observed elements from the database and propagate the modifications to the agent from which the SQ request was obtained in Step  800 . In one or more embodiments of the invention, the predetermined times may be periodic, e.g., every 5 seconds. In one or more embodiments of the invention, the predetermined times may be intermittent. 
     Thus, the methods shown in  FIG. 8A  may be used to generate observers, modifiers, and SQIs in response to requests from agents. 
       FIG. 8B  shows a flowchart in accordance with one or more embodiments of the invention. The method depicted in  FIG. 8B  may be used by a database to prevent a utilized storage capacity of a non-materialized table of the database from exceeding a maximum storage capacity of the non-materialized table in accordance with one or more embodiments of the invention. One or more steps shown in  FIG. 8B  may be omitted, repeated, and/or performed in a different order among different embodiments. 
     In Step  810 , a database of a network device obtains a storage capacity of a non-materialized table of a database. In one or more embodiments of the invention, the database may obtain the storage capacity of the non-materialized table by continuously monitoring the storage capacity. For example, the database may monitor the storage capacity after every time an entry of the non-materialized table is written and/or deleted. 
     In one or more embodiments of the invention, the database may obtain the storage capacity of the non-materialized table by intermittently monitoring the storage capacity of the non-materialized table. For example, the database may monitor the storage capacity periodically, e.g., ever 20 milliseconds. 
     In one or more embodiments of the invention, the non-materialized table may store output generated by a compiled query executing on the network device on which the database is stored. In one or more embodiments of the invention, the non-materialized table may store output generated by a compiled query executing on a network device that is different than the network device on which the database is stored. 
     In one or more embodiments of the invention, the storage capacity is a ratio of an available storage capacity of the non-materialized table to a total storage capacity of the non-materialized table. For example, if the non-materialized table included a total capacity of 100 entries and 75 of the entries were storing output, the storage capacity would be 0.25, e.g. (100−75)/100. 
     In Step  811 , the database determines whether the storage capacity of the non-materialized table exceeds a predetermined amount. In one or more embodiments of the invention, the predetermined amount is 0.1. In one or more embodiments of the invention, the predetermined amount is 0. If the storage capacity exceeds the predetermined amount, the method proceeds to Step  812 . If the storage capacity does not exceed the predetermined amount, the method proceeds to Step  810 . In other words, the database may monitor the storage capacity to determine whether the non-materialized table is close to being full, e.g., a fraction of the entries of the non-materialized table are storing output. 
     In Step  812 , the database may disable an upstream entity. An upstream entity may be any entity that contributes to the generation of output stored in the non-materialized table. 
     In one or more embodiments of the invention, the upstream entity may be a SQI that generates an output that is stored in the non-materialized output. Disabling the SQI may prevent additional output from being stored in the non-materialized table. In one or more embodiments of the invention, the database may disable a compiled query of the SQI that generates the output. 
     In one or more embodiments of the invention, the upstream entity may be an observer that triggers a SQI to generate output stored in the non-materialized table. Disabling the observer may prevent the SQI from generating output stored in the non-materialized table. 
     In one or more embodiments of the invention, the upstream entity may be a modifiers that stores an output of a SQI in the non-materialized table. Disabling the modifier may prevent the SQI from generating output which, in turn, prevents the output from being stored in the non-materialized table. 
     By disabling the upstream entity, additional output may be prevented from being stored in the non-materialized table and thereby prevent the storage capacity of the non-materialized table from exceeding a predetermined amount. 
     In Step  813 , the database increases a read rate of a downstream entity. A downstream entity may be any entity that consumes, e.g., reads, entries of the non-materialized output. Increasing the consumption rate of entries of the non-materialized table may prevent the storage capacity of the non-materialized table from exceeding the predetermined amount by causing the entries of the non-materialized entries to be deleted by the database after the entries are consumed. 
     In one or more embodiments of the invention, the downstream entity may be an observer that reads entries of the non-materialized table. 
     In one or more embodiments of the invention, the downstream entity may be a second SQI that generates a second output based on output stored in the non-materialized table. 
     In one or more embodiments of the invention, the downstream entity may be an agent that requested the output stored in the non-materialized table to be generated. The method may end following Step  813 . 
       FIG. 8C  shows a flowchart in accordance with one or more embodiments of the invention. The method depicted in  FIG. 8C  may be used to generate observers in response to requests for SQIs from agents in accordance with one or more embodiments of the invention. One or more steps shown in  FIG. 8C  may be omitted, repeated, and/or performed in a different order among different embodiments. 
     In Step  820 , a SQS manager of a network device obtains one or more input table targets. The input table targets may be one or more elements of a database on which a requested SQI is to operate. The input table targets may be obtained from a request from an agent requesting the SQI. 
     In Step  822 , the SQS manager selects one of the input table targets. 
     In Step  824 , the SQS manager determines the location of the input table target selected in Step  822 . The SQS manager may determine the location of the input table by target by requesting the location from a database planner ( 210 ,  FIG. 2 ) that manages the database ( 120 ,  FIG. 2 ). The location of the input table target may be an entry of a table of the database ( 120 ,  FIG. 2 ). 
     In Step  826 , the SQS manager generates an observer based on the location of the input table target. The location of the input table target may be located in the same address space as the input table of the SQI, located in a different address space than the input table of the SQI, or located in a different address space of a different network device than the input table of the SQI. The SQS manager may generate observers linked to memory transport protocols and/or inter-device memory transport protocols to facilitate propagating information from the database to the input table of a SQI. 
     For example, if an input table is located in a different address space than the input table of the SQI, the SQS manager may generate a first observer, in the address space of the input table target, linked to a memory transport protocol between the address space of the input table target and the address space of the input table. The SQS may generate a second observer, in the address space of the input table, linked to the memory transport protocol between the address space of the input table target and the address space of the input table and thereby propagate changes to the input table target to the input table. 
     In a second example, if an input table is located in a different address space of a different network device, the SQS manager may generate a first observer, in the address space of the different network device of the input table target, linked to an inter-device memory transport protocol between the different network device and the network device on which the input table exists. The SQS may generate a second observer, in the address space of the input table, linked to the inter-device memory transport protocol between the different network device and the network device on which the input table exists and thereby propagate changes to the input table target to the input table. 
     In Step  828 , the SQS manager determines whether all input table targets are observed by observers. If all input table targets are observed by observers, the method may end. If all input table targets are not observed by observers, the method may proceed to Step  822 . 
     Thus, the method shown in  FIG. 8C  may be used to generate observers to propagate changes to input table targets located in a database to an input table of a SQI. 
     While the method shown in  FIG. 8C  is illustrated as generating unique observers for each input table target, one of ordinary skill in the art will appreciate that the method may be implements by utilizing a single observer that observes multiple input table without departing from the invention. 
       FIG. 8D  shows a flowchart in accordance with one or more embodiments of the invention. The method depicted in  FIG. 8D  may be used to generate modifiers in response to requests for SQIs from agents in accordance with one or more embodiments of the invention. One or more steps shown in  FIG. 8D  may be omitted, repeated, and/or performed in a different order among different embodiments. 
     In Step  830 , a SQS manager of a network device obtains one or more output table targets. The output table targets may be one or more elements of a database on which a requested SQI is to propagate its output. The output table targets may be obtained from a request from an agent requesting the SQI. 
     In Step  832 , the SQS manager selects one of the output table targets. 
     In Step  834 , the SQS manager determines the location of the output table target selected in Step  832 . The SQS manager may determine the location of the output table target by requesting the location from a database planner ( 210 ,  FIG. 2 ) that manages the database ( 120 ,  FIG. 2 ). The location of the output table target may be an element of a table of the database ( 120 ,  FIG. 2 ). 
     In Step  836 , the SQS manager generates a modifier based on the location of the output table target. The modifier may write data received from the SQI to the location of the output table target, e.g., one or more elements of a table of the database. 
     In Step  838 , the SQS manager determines whether all output table targets have associated modifiers. If all output table targets have associated modifiers, the method may end. If all output table targets do not have associated modifiers, the method may proceed to Step  832 . 
     Thus, the method shown in  FIG. 8D  may be used to generate modifiers to propagate output generated by the SQI to an output table of a database. 
     While the method shown in  FIG. 8D  is illustrated as generating unique modifiers for each output table target, one of ordinary skill in the art will appreciate that the method may be implemented by utilizing a single modifier associated with all of the output table targets without departing from the invention. 
     As discussed with respect to  FIGS. 8C and 8D , observers and modifiers may be employed to read and/or write data to and/or from a database by a SQI. Similarly, observers and modifiers may be employed to read and/or write data to and/or from a database by an agent. 
       FIG. 8E  shows a flowchart in accordance with one or more embodiments of the invention. The method depicted in  FIG. 8E  may be used to generate observers in response to requests to read data from a database by an agent in accordance with one or more embodiments of the invention. One or more steps shown in  FIG. 8E  may be omitted, repeated, and/or performed in a different order among different embodiments. 
     In Step  840 , a database may obtain one or more observer targets. The database may obtain the observer targets based on a request from an agent. The request may include one or more elements of the database. 
     In Step  842 , the database may determine the location of the observer targets. The database may determine the location of the observer targets by requesting the location of each observer target from a database planner ( 210 ,  FIG. 2 ). 
     In Step  844 , the database may generate one or more observers based on the location of the observed targets. As described with respect to  FIG. 8B , multiple observers and/or memory transport may be used to propagate information from the observed targets of the database to the agent that requests the targets be observed in Step  840 . 
       FIG. 8F  shows a flowchart in accordance with one or more embodiments of the invention. The method depicted in  FIG. 8F  may be used to generate modifiers in response to requests to write data to a database by an agent in accordance with one or more embodiments of the invention. One or more steps shown in  FIG. 8F  may be omitted, repeated, and/or performed in a different order among different embodiments. 
     In Step  850 , a database may obtain one or more modifier targets. The database may obtain the modifier targets based on a request from an agent. The request may include one or more elements of the database. 
     In Step  842 , the database may determine the location of the modifier targets. The database may determine the location of the modifier targets by requesting the location of each modifier target from a database planner ( 210 ,  FIG. 2 ). 
     In Step  844 , the database may generate one or more modifiers based on the location of the modifier targets. 
       FIG. 9A  shows a flowchart in accordance with one or more embodiments of the invention. The method depicted in  FIG. 9A  may be used by an observer to notify a linked entity of a change to an observed element of a database in accordance with one or more embodiments of the invention. One or more steps shown in  FIG. 9A  may be omitted, repeated, and/or performed in a different order among different embodiments. 
     In Step  900 , an observer may obtain a modification to an observed table. As described with respect to  FIG. 5 , each element of each table may include a subscription list. When an element of a table of a database is modified, the database may notify each observer listed in the subscription list of the modification. The observer may obtain the modification by the notification of change provided by the database. 
     In one or more embodiments of the invention, the observer may periodically poll the database to determine whether an observed element of a table has been modified. The observer may determine whether the observed element of the table of the database has been modified based on the write history of the element. In other words, the observer may review the write history of the element since the element was last observed by the observer for modification. 
     In Step  910 , the observer may notify any linked entities of the modifications obtained in Step  900 . As described with respect to  FIGS. 7A and 8A , an observer may be linked to one or more entities. The entities may be input tables of SQIs, agents, or any other consumer of information. The observer may notify each linked entity of the modification of the element of the database the observer is observer is observing. 
       FIG. 9B  shows a flowchart in accordance with one or more embodiments of the invention. The method depicted in  FIG. 9B  may be used by a SQI to evaluate a SQ in accordance with one or more embodiments of the invention. One or more steps shown in  FIG. 9B  may be omitted, repeated, and/or performed in a different order among different embodiments. 
     In Step  920 , a SQI may obtain a modification to an input table. The modification may be obtained by an observer performing the method shown in  FIG. 9A . 
     In Step  930 , the SQI may execute the compiled query of the SQ in response to the modification. Executing the compiled query may generate output. 
     In Step  940 , the SQI may propagate output generated by evaluation of the SQI to an output table. The output generated by the SQI may be propagated to an output table by the method shown in  FIG. 9C . 
       FIG. 9C  shows a flowchart in accordance with one or more embodiments of the invention. The method depicted in  FIG. 9C  may be used by a modifier to propagate output in accordance with one or more embodiments of the invention. One or more steps shown in  FIG. 9C  may be omitted, repeated, and/or performed in a different order among different embodiments. 
     In Step  950 , a modifier may obtain an output. The modifier may obtain the output from a compiled query of a SQI, an agent, or any other entity. 
     In Step  960 , the modifier updates one or more linked tables based on the obtained output. 
       FIG. 10  shows a flowchart in accordance with one or more embodiments of the invention. The method depicted in  FIG. 10  may be used by a network device to manage a temporary storage in accordance with one or more embodiments of the invention. One or more steps shown in  FIG. 10  may be omitted, repeated, and/or performed in a different order among different embodiments. 
     In Step  1000 , a modifier of a SQI may obtain an output. The modifier may obtain the output from a compiled query of a SQI, an agent, or any other entity. 
     In Step  1010 , the modifier may store the output in a temporary storage of a database. 
     In Step  1020 , the database may receive a notification from an observer that an entity listed in a subscription list of the temporary storage has received the stored result. 
     In Step  1030 , the database may release the temporary storage. The database may release the temporary storage by deleting the stored result and/or storing other data in the temporary storage. 
     One or more embodiments of the invention may enable one or more of the following: i) storage of SQ results in a temporary storage, ii) determination of whether a SQI may be generated including a non-materialized output, iii) reduced memory use by storing output of SQIs in temporary storage, and iv) improved database performance by reducing the total number of stored entries. 
     While the invention has been described above with respect to a limited number of embodiments, those skilled in the art, having the benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.