Patent Publication Number: US-2018039513-A1

Title: Techniques and architectures for non-blocking parallel batching

Description:
TECHNICAL FIELD 
     Embodiments relate to event management in an event-based environment. More particularly, embodiments relate to techniques for efficiently managing data related to events from multiple sources. 
     BACKGROUND 
     Event-based environments manage data in response to events, some or all of which must be chronologically ordered. When and environment is responsible for data corresponding to a large number of events, management of that data can quickly become complex. Environments in which event-based data management quickly becomes complex can include, for example, a social media platform where many different parties and/or groups have independent feeds that can be interrelated and all be presented chronologically. Another example can include a sales environment in which information related to deals and/or the status of various components is tracked. 
     In these types of environments, data is continuously and rapidly pushed by many users to be stored in a backend storage system that can be remotely located across a network. Thus, a synchronous system can be quickly overwhelmed in an active environment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings in which like reference numerals refer to similar elements. 
         FIG. 1  is a block diagram of one embodiment of a parallel batching architecture. 
         FIG. 2  is a flow diagram of one embodiment of a parallel batching technique. 
         FIG. 3  is a flow diagram of one embodiment of a lane management technique. 
         FIG. 4  illustrates a block diagram of an environment where an on-demand database service might be used. 
         FIG. 5  illustrates another block diagram of an environment where an on-demand database service might be used. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth. However, embodiments of the invention may be practiced without these specific details. In other instances, well-known circuits, structures and techniques have not been shown in detail in order not to obscure the understanding of this description. 
     To address one or more of the shortcomings discussed above, batching and/or parallel operation can be supported. In one embodiment, event data can be topic based and each topic can be assigned a topic partition that can be managed independently of other topic partitions. In one embodiment, different topic partitions can be associated with different backend storage solutions (e.g., relational database, non-relational database). In one embodiment, a multi-layer retry mechanism is provided to provide elastic load management. 
     In one embodiment, in order to provide sufficient scaling, not only is batching utilized, but also parallelism in order to configure and manage bandwidth to the storage system. However, in an event-based environment, there is an order constraint posing difficulties to parallelism because dependent events must be processed in order. In one embodiment, an event is assigned a topic partition (aka, swim lane) in which data is inserted in the order in which it is received. 
     Various embodiments described herein conceptually operate utilizing the concept of a virtual swim lane. Within a swim lane events that are received are processed in order, thus maintaining event ordering. However, swim lanes are independent of each other so that timing constraints are imposed between swim lanes. That is, an event in one swim lane may be received after an event in another swim lane but can be processes before. 
     In one embodiment, the event-based environment provides a number of “swim lanes” that topics/events are assigned to. In one embodiment, the topics/events are hashed into the swim lanes to help achieve a level of parallelism while satisfying ordering constraints. In some embodiments, the number of swim lanes can be configured when the environment is established or otherwise periodically modified. That is, the number of swim lanes can be generally static. In other embodiments, the number of swim lanes can be dynamically modified based on various factors. For example, an environment can be configured to  100  swim lanes to support an unlimited number of topics, each of which can be assigned to one of the swim lanes via, for example, hashing. 
     In one embodiment, each swim lane represents a channel or connection to one or more storage systems. This configuration allows control over the bandwidth to and from the storage system(s). Because the same topic is consistently hashed to the same swim lane, ordering of data and/or events is maintained for each topic, but data and/or events for different topics can be processed in parallel, which provides parallelism within the system. 
     In one embodiment, for each swim lane, data can be queued until the queue reaches one or more pre-selected thresholds (e.g., a pre-selected level and/or a pre-selected time has passed). In one embodiment, when one or more of these triggers are reached, data and/or events can be sent in bulk to the storage system(s). That is, the batching functionality can be controlled by size and/or time, both of which can be configurable. With these controls, data processing/storage latency and responsiveness can be controlled. 
     In one embodiment, when one or more of the thresholds is reached, a batch is handed over to another scheduler that is responsible to send the batch to the storage system(s) while the queuing system can continue to manage new events and data for subsequent batches. 
     In one embodiment, the system can track the number of outstanding outbound batches for each lane. In one embodiment, when the number of outstanding batches reaches a pre-selected threshold, the system can be stalled by denying access and/or new inputs to one or more lanes. In one embodiment, a configurable retry mechanism can be provided to slow down incoming events and/or data efficiently without shutting down access. 
     Because the retry mechanism is configurable and flexible, in high-load cases, users can experience a natural slow down and ramping back up again when the system recovers rather than being blocked from service. In one embodiment, the retry mechanism employs an exponential back off strategy. In another embodiment, the retry mechanism employs a Fibonacci back off strategy. 
       FIG. 1  is a block diagram of one embodiment of a parallel batching architecture. Architecture  100  can part of a single hardware computing device or can be distributed across multiple hardware computing devices. 
     In one embodiment, event sources (e.g.,  110 ,  112 , . . .  118 ) can provide data and/or event information from one or more environments. For example, events can be comments and responses in a social media environment, sales events/activities, organizational changes, real-time environmental data, system data logging, etc. Event sources can be any hardware computing device or interface capable of receiving data corresponding to an event. 
     Mapping agent  120  operates to analyze event data and determine via an identifier or other indication an event to which the data corresponds. For example, in a social media setting, an initial post can be a new event and responses to the initial post are part of the event and should be processed in the correct order. As another social media example, creation of a profile can be a new event and posts within that profile can be considered part of the event and be processed in the correct order. 
     Mapping agent  120  operates to map event information to the appropriate lane agent (e.g.,  140 ,  145 ). In one embodiment, mapping agent  120  performs this function by utilizing a hashing function or other mapping strategy. Mapping agent  120  causes the event-related data to be assigned to the proper lane agent in event manager  130 . 
     In one embodiment, the lane agents manage queues for processing events/data from a specific event identifiers. That is, mapping agent  120  maps incoming events to lane agents through which the swim lane concept is managed/enforced. In one embodiment, the lane agents coordinate sending batches of data to corresponding storage devices (e.g.,  180 ,  185 ). In one embodiment, data within a swim lane (as managed by a lane agent) is managed in batches by size and elapsed time, both of which can be configurable. For example, a queue depth of 50 events or 500 ms, which ever happens first, can be a trigger to process the batch. Additional and/or different characteristics can be used as triggers. Configuration of various triggers and thresholds can allow for optimization of latency and bandwidth. 
     In one embodiment, each lane agent is communicatively coupled with a corresponding storage device/partition. The storage device(s) can be individual storage devices (e.g., hard disks, flash drives, solid state devices), or they can be partitions or segments of storage devices so that multiple lanes can be serviced by a single physical device, or some combination thereof. Lane agents can operate independently of each other so that processing of different events can occur in parallel, which can improve system efficiency. In various embodiments, architecture  100  can include additional and/or different components, for example, processor(s)  150  and/or memory controller(s)  155 . 
     In one embodiment, the storage devices can be different types of storage devices. For example, in an embodiment, one storage device can be a SQL database and another storage device can be an HBASE database. Any combination of storage structures can be supported. 
       FIG. 2  is a flow diagram of one embodiment of a parallel batching technique. The process described with respect to  FIG. 2  can be performed, for example, by mapping agent  120  and or event manager  130  of  FIG. 1 . Other architectures can also be configured to perform the functions described with respect to  FIG. 2 . 
     Event information is received,  210 . This event information can be received from, for example, one or more remote devices (e.g., tablet, desktop computer, smartphone, laptop computer). In one embodiment, the event information can be received by the host computing platform via an application program interface (API) configured to receive and process event information. 
     For example, a first electronic device can be used by a first user to post a comment to social media site and a second electronic device can be use by a second user to post another comment to the social media site. The comments can be received by the host computing platform and processed as described herein. 
     In one embodiment, the received events are mapped to a topic partition (swim lane),  220 . In one embodiment, the mapping is accomplished by using a hashing function; however, other mapping strategies can also be utilized. As described above, each topic partition has a corresponding lane agent (topic partition agent) that receives the events of the topic partition and manages the processing of those events. 
     In one embodiment, the events are mapped to the topic partition,  220 , by, for example the mapping agent of  FIG. 1 . In one embodiment, mapping is performed based on an event identifier or other information within the event. 
     In one embodiment, the lane agent manages the queuing of event for the corresponding topic partition,  230 . As discussed above, any number of topic partitions can be supported and the topic partitions can be processed independently of each other. The lane agents function to manage the ordering (if necessary) and queuing of events for the assigned topic partition and can function without regard to the processing of events for other topic partitions handled by other lane agents. 
     If one or more thresholds have not been reached,  240 , receiving and queuing of subsequent events occurs. If one or more thresholds have been reached,  240 , events stored in the queue are batched and sent to a scheduler,  250 , to be sent to storage. Because the lane agents do not manage the scheduling, queuing of events for the next batch is not stalled while the scheduling functionality is performed by the lane agent. 
       FIG. 3  is a flow diagram of one embodiment of a lane management technique. The process described with respect to  FIG. 3  can be performed, for example, event manager  130  of  FIG. 1 . Other architectures can also be configured to perform the functions described with respect to  FIG. 3 . Because the triggers that cause a batch to be dequeued can be based on time, queue size and/or other characteristics, the batch size may not be consistent, but may have a maximum allowable size. 
     Events are received for the specific topic partition (swim lane) being managed,  310 . As discussed above, a mapping agent (or other entity) analyzes events to determine which topic partition should receive the event. This can be based on, for example, hashing an event identifier or other information. Topic partitions can be managed independently of each other. 
     The event manager queues the received events in the proper order,  320 . Because events have a time based ordering, events should be queued in the appropriate order. If any adjusting of the ordering is necessary, the lane agent can adjust the ordering in the queue as necessary. 
     If one or more thresholds have not been reached,  330 , receiving and queuing of subsequent events occurs. If one or more thresholds have been reached,  330 , events stored in the queue are batched,  340 . The batched events are then sent to a scheduler,  350 , to be sent to storage. 
       FIG. 4  illustrates a block diagram of an environment  410  wherein an on-demand database service might be used. Environment  410  may include user systems  412 , network  414 , system  416 , processor system  417 , application platform  418 , network interface  420 , tenant data storage  422 , system data storage  424 , program code  426 , and process space  428 . In other embodiments, environment  410  may not have all of the components listed and/or may have other elements instead of, or in addition to, those listed above. 
     Environment  410  is an environment in which an on-demand database service exists. User system  412  may be any machine or system that is used by a user to access a database user system. For example, any of user systems  412  can be a handheld computing device, a mobile phone, a laptop computer, a work station, and/or a network of computing devices. As illustrated in herein  FIG. 4  (and in more detail in  FIG. 5 ) user systems  412  might interact via a network  414  with an on-demand database service, which is system  416 . 
     An on-demand database service, such as system  416 , is a database system that is made available to outside users that do not need to necessarily be concerned with building and/or maintaining the database system, but instead may be available for their use when the users need the database system (e.g., on the demand of the users). Some on-demand database services may store information from one or more tenants stored into tables of a common database image to form a multi-tenant database system (MTS). Accordingly, “on-demand database service  416 ” and “system  416 ” will be used interchangeably herein. A database image may include one or more database objects. A relational database management system (RDMS) or the equivalent may execute storage and retrieval of information against the database object(s). Application platform  418  may be a framework that allows the applications of system  416  to run, such as the hardware and/or software, e.g., the operating system. In an embodiment, on-demand database service  416  may include an application platform  418  that enables creation, managing and executing one or more applications developed by the provider of the on-demand database service, users accessing the on-demand database service via user systems  412 , or third party application developers accessing the on-demand database service via user systems  412 . 
     The users of user systems  412  may differ in their respective capacities, and the capacity of a particular user system  412  might be entirely determined by permissions (permission levels) for the current user. For example, where a salesperson is using a particular user system  412  to interact with system  416 , that user system has the capacities allotted to that salesperson. However, while an administrator is using that user system to interact with system  416 , that user system has the capacities allotted to that administrator. In systems with a hierarchical role model, users at one permission level may have access to applications, data, and database information accessible by a lower permission level user, but may not have access to certain applications, database information, and data accessible by a user at a higher permission level. Thus, different users will have different capabilities with regard to accessing and modifying application and database information, depending on a user&#39;s security or permission level. 
     Network  414  is any network or combination of networks of devices that communicate with one another. For example, network  414  can be any one or any combination of a LAN (local area network), WAN (wide area network), telephone network, wireless network, point-to-point network, star network, token ring network, hub network, or other appropriate configuration. As the most common type of computer network in current use is a TCP/IP (Transfer Control Protocol and Internet Protocol) network, such as the global internetwork of networks often referred to as the “Internet” with a capital “I,” that network will be used in many of the examples herein. However, it should be understood that the networks that one or more implementations might use are not so limited, although TCP/IP is a frequently implemented protocol. 
     User systems  412  might communicate with system  416  using TCP/IP and, at a higher network level, use other common Internet protocols to communicate, such as HTTP, FTP, AFS, WAP, etc. In an example where HTTP is used, user system  412  might include an HTTP client commonly referred to as a “browser” for sending and receiving HTTP messages to and from an HTTP server at system  416 . Such an HTTP server might be implemented as the sole network interface between system  416  and network  414 , but other techniques might be used as well or instead. In some implementations, the interface between system  416  and network  414  includes load sharing functionality, such as round-robin HTTP request distributors to balance loads and distribute incoming HTTP requests evenly over a plurality of servers. At least as for the users that are accessing that server, each of the plurality of servers has access to the MTS&#39; data; however, other alternative configurations may be used instead. 
     In one embodiment, system  416 , shown in  FIG. 4 , implements a web-based customer relationship management (CRM) system. For example, in one embodiment, system  416  includes application servers configured to implement and execute CRM software applications as well as provide related data, code, forms, webpages and other information to and from user systems  412  and to store to, and retrieve from, a database system related data, objects, and Webpage content. With a multi-tenant system, data for multiple tenants may be stored in the same physical database object, however, tenant data typically is arranged so that data of one tenant is kept logically separate from that of other tenants so that one tenant does not have access to another tenant&#39;s data, unless such data is expressly shared. In certain embodiments, system  416  implements applications other than, or in addition to, a CRM application. For example, system  416  may provide tenant access to multiple hosted (standard and custom) applications, including a CRM application. User (or third party developer) applications, which may or may not include CRM, may be supported by the application platform  418 , which manages creation, storage of the applications into one or more database objects and executing of the applications in a virtual machine in the process space of the system  416 . 
     One arrangement for elements of system  416  is shown in  FIG. 4 , including a network interface  420 , application platform  418 , tenant data storage  422  for tenant data  423 , system data storage  424  for system data  425  accessible to system  416  and possibly multiple tenants, program code  426  for implementing various functions of system  416 , and a process space  428  for executing MTS system processes and tenant-specific processes, such as running applications as part of an application hosting service. Additional processes that may execute on system  416  include database indexing processes. 
     Several elements in the system shown in  FIG. 4  include conventional, well-known elements that are explained only briefly here. For example, each user system  412  could include a desktop personal computer, workstation, laptop, PDA, cell phone, or any wireless access protocol (WAP) enabled device or any other computing device capable of interfacing directly or indirectly to the Internet or other network connection. User system  412  typically runs an HTTP client, e.g., a browsing program, such as Microsoft&#39;s Internet Explorer browser, Netscape&#39;s Navigator browser, Opera&#39;s browser, or a WAP-enabled browser in the case of a cell phone, PDA or other wireless device, or the like, allowing a user (e.g., subscriber of the multi-tenant database system) of user system  412  to access, process and view information, pages and applications available to it from system  416  over network  414 . Each user system  412  also typically includes one or more user interface devices, such as a keyboard, a mouse, trackball, touch pad, touch screen, pen or the like, for interacting with a graphical user interface (GUI) provided by the browser on a display (e.g., a monitor screen, LCD display, etc.) in conjunction with pages, forms, applications and other information provided by system  416  or other systems or servers. For example, the user interface device can be used to access data and applications hosted by system  416 , and to perform searches on stored data, and otherwise allow a user to interact with various GUI pages that may be presented to a user. As discussed above, embodiments are suitable for use with the Internet, which refers to a specific global internetwork of networks. However, it should be understood that other networks can be used instead of the Internet, such as an intranet, an extranet, a virtual private network (VPN), a non-TCP/IP based network, any LAN or WAN or the like. 
     According to one embodiment, each user system  412  and all of its components are operator configurable using applications, such as a browser, including computer code run using a central processing unit such as an Intel Pentium® processor or the like. Similarly, system  416  (and additional instances of an MTS, where more than one is present) and all of their components might be operator configurable using application(s) including computer code to run using a central processing unit such as processor system  417 , which may include an Intel Pentium® processor or the like, and/or multiple processor units. A computer program product embodiment includes a machine-readable storage medium (media) having instructions stored thereon/in which can be used to program a computer to perform any of the processes of the embodiments described herein. Computer code for operating and configuring system  416  to intercommunicate and to process webpages, applications and other data and media content as described herein are preferably downloaded and stored on a hard disk, but the entire program code, or portions thereof, may also be stored in any other volatile or non-volatile memory medium or device as is well known, such as a ROM or RAM, or provided on any media capable of storing program code, such as any type of rotating media including floppy disks, optical discs, digital versatile disk (DVD), compact disk (CD), microdrive, and magneto-optical disks, and magnetic or optical cards, nanosystems (including molecular memory ICs), or any type of media or device suitable for storing instructions and/or data. Additionally, the entire program code, or portions thereof, may be transmitted and downloaded from a software source over a transmission medium, e.g., over the Internet, or from another server, as is well known, or transmitted over any other conventional network connection as is well known (e.g., extranet, VPN, LAN, etc.) using any communication medium and protocols (e.g., TCP/IP, HTTP, HTTPS, Ethernet, etc.) as are well known. It will also be appreciated that computer code for implementing embodiments can be implemented in any programming language that can be executed on a client system and/or server or server system such as, for example, C, C++, HTML, any other markup language, Java™, JavaScript, ActiveX, any other scripting language, such as VBScript, and many other programming languages as are well known may be used. (Java™ is a trademark of Sun Microsystems, Inc.). 
     According to one embodiment, each system  416  is configured to provide webpages, forms, applications, data and media content to user (client) systems  412  to support the access by user systems  412  as tenants of system  416 . As such, system  416  provides security mechanisms to keep each tenant&#39;s data separate unless the data is shared. If more than one MTS is used, they may be located in close proximity to one another (e.g., in a server farm located in a single building or campus), or they may be distributed at locations remote from one another (e.g., one or more servers located in city A and one or more servers located in city B). As used herein, each MTS could include one or more logically and/or physically connected servers distributed locally or across one or more geographic locations. Additionally, the term “server” is meant to include a computer system, including processing hardware and process space(s), and an associated storage system and database application (e.g., OODBMS or RDBMS) as is well known in the art. It should also be understood that “server system” and “server” are often used interchangeably herein. Similarly, the database object described herein can be implemented as single databases, a distributed database, a collection of distributed databases, a database with redundant online or offline backups or other redundancies, etc., and might include a distributed database or storage network and associated processing intelligence. 
       FIG. 5  also illustrates environment  410 . However, in  FIG. 5  elements of system  416  and various interconnections in an embodiment are further illustrated.  FIG. 5  shows that user system  412  may include processor system  412 A, memory system  412 B, input system  412 C, and output system  412 D.  FIG. 5  shows network  414  and system  416 .  FIG. 5  also shows that system  416  may include tenant data storage  422 , tenant data  423 , system data storage  424 , system data  425 , User Interface (UI)  530 , Application Program Interface (API)  532 , PL/SOQL  534 , save routines  536 , application setup mechanism  538 , applications servers  500   1 - 400   N , system process space  502 , tenant process spaces  504 , tenant management process space  510 , tenant storage area  512 , user storage  514 , and application metadata  516 . In other embodiments, environment  410  may not have the same elements as those listed above and/or may have other elements instead of, or in addition to, those listed above. 
     User system  412 , network  414 , system  416 , tenant data storage  422 , and system data storage  424  were discussed above in  FIG. 4 . Regarding user system  412 , processor system  412 A may be any combination of one or more processors. Memory system  412 B may be any combination of one or more memory devices, short term, and/or long term memory. Input system  412 C may be any combination of input devices, such as one or more keyboards, mice, trackballs, scanners, cameras, and/or interfaces to networks. Output system  412 D may be any combination of output devices, such as one or more monitors, printers, and/or interfaces to networks. As shown by  FIG. 5 , system  416  may include a network interface  420  (of  FIG. 4 ) implemented as a set of HTTP application servers  500 , an application platform  418 , tenant data storage  422 , and system data storage  424 . Also shown is system process space  502 , including individual tenant process spaces  504  and a tenant management process space  510 . Each application server  500  may be configured to tenant data storage  422  and the tenant data  423  therein, and system data storage  424  and the system data  425  therein to serve requests of user systems  412 . The tenant data  423  might be divided into individual tenant storage areas  512 , which can be either a physical arrangement and/or a logical arrangement of data. Within each tenant storage area  512 , user storage  514  and application metadata  516  might be similarly allocated for each user. For example, a copy of a user&#39;s most recently used (MRU) items might be stored to user storage  514 . Similarly, a copy of MRU items for an entire organization that is a tenant might be stored to tenant storage area  512 . A UI  530  provides a user interface and an API  532  provides an application programmer interface to system  416  resident processes to users and/or developers at user systems  412 . The tenant data and the system data may be stored in various databases, such as one or more Oracle™ databases. 
     Application platform  418  includes an application setup mechanism  538  that supports application developers&#39; creation and management of applications, which may be saved as metadata into tenant data storage  422  by save routines  536  for execution by subscribers as one or more tenant process spaces  504  managed by tenant management process  510  for example. Invocations to such applications may be coded using PL/SOQL  534  that provides a programming language style interface extension to API  532 . A detailed description of some PL/SOQL language embodiments is discussed in commonly owned U.S. Pat. No. 7,730,478 entitled, “Method and System for Allowing Access to Developed Applicants via a Multi-Tenant Database On-Demand Database Service”, issued Jun. 1, 2010 to Craig Weissman, which is incorporated in its entirety herein for all purposes. Invocations to applications may be detected by one or more system processes, which manage retrieving application metadata  516  for the subscriber making the invocation and executing the metadata as an application in a virtual machine. 
     Each application server  500  may be communicably coupled to database systems, e.g., having access to system data  425  and tenant data  423 , via a different network connection. For example, one application server  500   1  might be coupled via the network  414  (e.g., the Internet), another application server  500   N-1  might be coupled via a direct network link, and another application server  500   N  might be coupled by yet a different network connection. Transfer Control Protocol and Internet Protocol (TCP/IP) are typical protocols for communicating between application servers  500  and the database system. However, it will be apparent to one skilled in the art that other transport protocols may be used to optimize the system depending on the network interconnect used. 
     In certain embodiments, each application server  500  is configured to handle requests for any user associated with any organization that is a tenant. Because it is desirable to be able to add and remove application servers from the server pool at any time for any reason, there is preferably no server affinity for a user and/or organization to a specific application server  500 . In one embodiment, therefore, an interface system implementing a load balancing function (e.g., an F5 Big-IP load balancer) is communicably coupled between the application servers  500  and the user systems  412  to distribute requests to the application servers  500 . In one embodiment, the load balancer uses a least connections algorithm to route user requests to the application servers  500 . Other examples of load balancing algorithms, such as round robin and observed response time, also can be used. For example, in certain embodiments, three consecutive requests from the same user could hit three different application servers  500 , and three requests from different users could hit the same application server  500 . In this manner, system  416  is multi-tenant, wherein system  416  handles storage of, and access to, different objects, data and applications across disparate users and organizations. 
     As an example of storage, one tenant might be a company that employs a sales force where each salesperson uses system  416  to manage their sales process. Thus, a user might maintain contact data, leads data, customer follow-up data, performance data, goals and progress data, etc., all applicable to that user&#39;s personal sales process (e.g., in tenant data storage  422 ). In an example of a MTS arrangement, since all of the data and the applications to access, view, modify, report, transmit, calculate, etc., can be maintained and accessed by a user system having nothing more than network access, the user can manage his or her sales efforts and cycles from any of many different user systems. For example, if a salesperson is visiting a customer and the customer has Internet access in their lobby, the salesperson can obtain critical updates as to that customer while waiting for the customer to arrive in the lobby. 
     While each user&#39;s data might be separate from other users&#39; data regardless of the employers of each user, some data might be organization-wide data shared or accessible by a plurality of users or all of the users for a given organization that is a tenant. Thus, there might be some data structures managed by system  416  that are allocated at the tenant level while other data structures might be managed at the user level. Because an MTS might support multiple tenants including possible competitors, the MTS should have security protocols that keep data, applications, and application use separate. Also, because many tenants may opt for access to an MTS rather than maintain their own system, redundancy, up-time, and backup are additional functions that may be implemented in the MTS. In addition to user-specific data and tenant specific data, system  416  might also maintain system level data usable by multiple tenants or other data. Such system level data might include industry reports, news, postings, and the like that are sharable among tenants. 
     In certain embodiments, user systems  412  (which may be client systems) communicate with application servers  500  to request and update system-level and tenant-level data from system  416  that may require sending one or more queries to tenant data storage  422  and/or system data storage  424 . System  416  (e.g., an application server  500  in system  416 ) automatically generates one or more SQL statements (e.g., one or more SQL queries) that are designed to access the desired information. System data storage  424  may generate query plans to access the requested data from the database. 
     Each database can generally be viewed as a collection of objects, such as a set of logical tables, containing data fitted into predefined categories. A “table” is one representation of a data object, and may be used herein to simplify the conceptual description of objects and custom objects. It should be understood that “table” and “object” may be used interchangeably herein. Each table generally contains one or more data categories logically arranged as columns or fields in a viewable schema. Each row or record of a table contains an instance of data for each category defined by the fields. For example, a CRM database may include a table that describes a customer with fields for basic contact information such as name, address, phone number, fax number, etc. Another table might describe a purchase order, including fields for information such as customer, product, sale price, date, etc. In some multi-tenant database systems, standard entity tables might be provided for use by all tenants. For CRM database applications, such standard entities might include tables for Account, Contact, Lead, and Opportunity data, each containing pre-defined fields. It should be understood that the word “entity” may also be used interchangeably herein with “object” and “table”. 
     In some multi-tenant database systems, tenants may be allowed to create and store custom objects, or they may be allowed to customize standard entities or objects, for example by creating custom fields for standard objects, including custom index fields. U.S. patent application Ser. No. 10/817,161, filed Apr. 2, 2004, entitled “Custom Entities and Fields in a Multi-Tenant Database System”, and which is hereby incorporated herein by reference, teaches systems and methods for creating custom objects as well as customizing standard objects in a multi-tenant database system. In certain embodiments, for example, all custom entity data rows are stored in a single multi-tenant physical table, which may contain multiple logical tables per organization. It is transparent to customers that their multiple “tables” are in fact stored in one large table or that their data may be stored in the same table as the data of other customers. 
     Reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment. 
     While the invention has been described in terms of several embodiments, those skilled in the art will recognize that the invention is not limited to the embodiments described, but can be practiced with modification and alteration within the spirit and scope of the appended claims. The description is thus to be regarded as illustrative instead of limiting.