Patent Publication Number: US-11394780-B2

Title: System and method for facilitating deduplication of operations to be performed

Description:
RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 15/875,285, filed Oct. 16, 2017, which is a continuation of U.S. patent application Ser. No. 13/874,381, filed Apr. 30, 2013, now U.S. Pat. No. 9,819,728, which claims priority to U.S. Provisional Application No. 61/640,632, filed Apr. 30, 2012, the disclosures of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The disclosed implementations relate generally to facilitating deduplication of operations to be performed. 
     BACKGROUND 
     In a distributed computing system, a plurality of servers are used to provide load balancing and/or provide low-latency points of access to nearby computer systems. For example, in a distributed storage system, data is replicated in storage clusters that are located across multiple geographical locations. In doing so, the availability of the data is increased and the network proximity of the data to client computer systems is decreased. When a large object, such as a video file, is uploaded to a storage cluster in a distributed storage system, other objects with identical content may already exist in the distributed storage system. Furthermore, if the object becomes popular, multiple instances of the object may be uploaded around the same time (e.g., via email attachments) to multiple storage clusters in the distributed storage system. To avoid unnecessarily duplicating use of resources in a distributed computing system, deduplication techniques may be used. For example, deduplication techniques may be used to ensure that only one replica of the content for a plurality of identical objects is stored in the same storage cluster and that the plurality of identical objects are not unnecessarily replicated to other storage clusters. However, deduplication techniques cannot be easily applied across the distributed computing system. 
     SUMMARY 
     According to some implementations, deduplication of operations is performed by a server having at least one processor and memory. The memory stores at least one program for execution by the at least one processor. The server receives an operation to be performed, and applies a mapping function to at least one parameter of the operation. The mapping function produces a mapping value in a target mapping space. The target mapping space is partitioned among a plurality of target servers, where the partition for each respective target server is proportional to the respective resource capacity of the respective target server. The server identifies a target server in the set of target servers whose portion of the target mapping space includes the mapping value, and issues the operation to the target server. 
     According to some implementations, prior to applying the mapping function to the at least one parameter of the operation, the server also: obtains the resource capacities of the target servers in the set of target servers; and partitions the target mapping space among the target servers in the set of target servers proportionally to the resource capacities of the target servers in the set of target servers. 
     According to some implementations, the server determines that at least one target server in the set of target servers has become unavailable. In this case, the server partitions the portion of the target mapping space associated with the at least one target server among the remaining target servers in the set of target servers proportionally to the resource capacities of the remaining target servers in the set of target servers. 
     According to some implementations, the mapping function is usable to map respective parameters of a respective operation to a respective mapping value in the target mapping space. 
     According to some implementations, the mapping function is a hash function. 
     According to some implementations, the operation includes a request to perform a search query, and the at least one parameter includes the search query. 
     According to some implementations, the operation includes a request to perform a search query, and the resource capacity of each respective target server includes the number of queries per second that the respective target server can process. 
     According to some implementations, the operation includes a request to write data to a target server, and the at least one parameter includes the data. 
     According to some implementations, the operation includes a request to write data to a target server, and the resource capacity of each respective target server includes the remaining amount of available storage space on the respective target server. 
     According to some implementations, a system is provided to facilitate deduplication of operations to be performed. The system includes at least one processor and memory. One or more programs are stored in the memory, and are executable by the at least one processor. The programs include executable instructions. The programs include instructions to receive an operation to be performed. The programs also include instructions to apply a mapping function to at least one parameter of the operation. The mapping function produces a mapping value in a target mapping space. The target mapping space is partitioned among target servers in a set of target servers proportionally to the resource capacities of the target servers. The programs include instructions to identify a target server in the set of target servers whose portion of the target mapping space includes the mapping value, and to issue the operation to the target server. 
     According to some implementations, a non-transitory computer readable storage medium stores one or more programs configured for execution by at least one processor of a computer system. The programs include instructions to receive an operation to be performed. The programs also include instructions to apply a mapping function to at least one parameter of the operation. The mapping function produces a mapping value in a target mapping space, where the target mapping space is partitioned among target servers in a set of target servers proportionally to the resource capacities of the target servers. The programs include instructions to identify a target server in the set of target servers whose portion of the target mapping space includes the mapping value, and to issue the operation to the target server. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The implementations disclosed herein are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings. Like reference numerals refer to corresponding parts throughout the drawings. 
         FIG. 1  is a block diagram illustrating a network system, according to some implementations. 
         FIG. 2A  is a block diagram illustrating an example target mapping space, according to some implementations. 
         FIG. 2B  is a block diagram illustrating another example target mapping space, according to some implementations. 
         FIG. 3  is a block diagram illustrating an example process for issuing an operation, according to some implementations. 
         FIG. 4  is a block diagram illustrating a server, according to some implementations. 
         FIG. 5  is a block diagram illustrating a target server, according to some implementations. 
         FIG. 6  is a block diagram illustrating a client computer system, according to some implementations. 
         FIG. 7  is a flowchart of a method for issuing operations to be performed, according to some implementations. 
         FIG. 8  is a flowchart of a method for partitioning a target mapping space, according to some implementations. 
         FIG. 9  is a flowchart of a method for partitioning a portion of a target mapping space associated with a particular target server, according to some implementations. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a block diagram illustrating a network system  100 , according to some implementations. The network system  100  includes a server  102 , a plurality of target servers  104 - 1  to  104 -N, and a client computer system  106  coupled to network  120 . In some implementations, the target servers  104 - 1  to  104 -N are targets of operations that the server  102  issues. For example, the server  102  may issue a read operation to one of the target servers  104 - 1  to  104 -N to read data stored on one of the target servers  104 - 1  to  104 -N. In another example, the server  102  may issue a write operation to one of the target servers  104 - 1  to  104 -N to write data to one of the target servers  104 - 1  to  104 -N. Other operations that the server  102  may issue, include, but are not limited to, an operation to delete data stored on a target server, an operation to update data stored on a target server, an operation to perform a search query, and any operations involving data. Note that the term “data” is used in this specification to include any type of data (e.g., binary, text, etc.) and also includes metadata (e.g., data about the data). 
     In some implementations, a respective target server is a compute node in a compute cluster of a distributed computing system. Note that a compute node includes one or more computer systems including one or more processors that provides computational resources for other computer systems. In some implementations, a respective target server is a storage node in a storage cluster of a distributed storage system. In some implementations, the respective target server is a local server (e.g., in the same data center, the same building, and/or the same geographic location, etc., as the server  102 ). In some implementations, the respective target server is a remote server (e.g., in a different data center, different building, and/or different geographic location, etc., as the server  102 ). 
     In some implementations, the server  102  is a compute node in a compute cluster of the distributed computing system. In some implementations, the server  102  is a storage node in a storage cluster of the distributed storage system. 
     The client computer system  106  includes, but is not limited to, a desktop computer system, a laptop computer system, a smart phone, a mobile phone, a tablet computer system, a server, a game console, a set top box, a television set, and any device that can transmit and/or receive data via network  120 . 
     Network  120  may generally include any type of wired or wireless communication channel capable of coupling together computing nodes. This includes, but is not limited to, a local area network, a wide area network, or a combination of networks. In some implementations, network  120  includes the Internet. 
     Note that although  FIG. 1  shows one instance of the server  102 , multiple servers may be present in the network system  100 . For example, the server  102  may include a plurality of distributed servers. Similarly, each of the target servers  104  may represent multiple target servers. For example, the target server  104 - 1  may include a plurality of distributed servers. Distributed servers may provide load balancing and/or may provide low-latency points of access to nearby computer systems. The distributed servers may be located within a single location (e.g., a data center, a building, etc.) or may be geographically distributed across multiple locations (e.g., data centers at various geographical locations, etc.). Also note that although the implementations described herein refer to the server  102 , the implementations may be applied to multiple servers. Furthermore, note that the term “server” and “target server” are relative terms that are interchangeable. In this specification, the term “server” is used to refer to a computer system (e.g., the server  102 ) that issues an operation to on another computer system (e.g., the target server  104 - 1 , the client computer system  106 ). Thus, in some instances, the server  102  may be the computer system that issues operations to another computer system (e.g., the target server  104 - 1 ). In other instances, the target server  104 - 1  (or another one of the target server  104 - 2  to  104 -N, the client computer system  106 , etc.) may be the computer system that issues operations to another computer system (e.g., the server  102 , the target servers  104 - 2  to  104 -N, etc.). 
     As discussed above, deduplication techniques cannot easily be applied across a distributed computing system. Typically, one compute cluster (or one storage cluster) does not know whether another computer cluster (or another storage cluster) has previously received and processed (and/or executed) the operation. To address these deficiencies, in some implementations, when the server  102  receives an operation to be performed, the server  102  applies a mapping function to at least one parameter of the operation to produce a mapping value in a target mapping space, which maps mapping values to target servers (e.g., in the distributed computing system). The at least one parameter of the operation includes, but is not limited to, a type of the operation (e.g., read, write, update, search, etc.), data (e.g., content such as audio files, video files, documents, text, images, etc.) included in the operation (e.g., the data to be written, a search query, etc.), an identifier for data associated with the operation (e.g., an object identifier, etc.), a network address (or other identifier) of the computer system from which the operation was received, and a network address (or other identifier) for the server  102 . The target mapping space is partitioned between target servers proportional to resource capacities of the target servers. In some implementations, the resource capacities of a respective target server include the available or remaining resource capacities of the respective target server. The server  102  then identifies a target server using the mapping value and the target mapping space and issues the operation to the target server. When the server  102  (or another server) receives the same operation, or alternatively a request for which the at least one parameter of the operation is the same as a previously received operation (e.g., the data/content of the operation is the same), the mapping value will be the same and the same target server is identified. Thus, the same operation is issued to the same target server and deduplication techniques may be performed on (or by) the target server (the compute cluster, the storage cluster, etc.) to reduce duplication of data any or compute resources. For example, a search query that was issued previously to the same target server does not need to be performed by the target server again. Similarly, a video file that was previously stored on the target server does not need to be stored on the target server again. These embodiments are described in more detail below. 
       FIG. 2A  is a block diagram illustrating an example target mapping space, according to some implementations. In the example illustrated in  FIG. 2A , the set of target servers includes target servers  104 - 1 ,  104 - 2 ,  104 - 3 ,  104 - 4 , and  104 - 5 . The resource capacities (e.g., the available or remaining resource capacities) include the amount of storage that is available for use (or that is remaining) on the target servers. The amount of storage that is available for use on each target server is as follows: 40 TB for target server  104 - 1 , 24 TB for target server  104 - 2 , 56 TB for target server  104 - 3 , 8 TB for target server  104 - 4 , and 72 TB for target server  104 - 5 . In some implementations, the target mapping space is partitioned between the target servers proportional to resource capacities of the target servers. In the example illustrated in  FIG. 2A , the total amount of storage that is available for use across the target servers  104 - 1  to  104 - 5  is 200 TB. Thus, in these implementations, the target mapping space is partitioned between the target servers as follows: 20% of the target mapping space is allocated to the target server  104 - 1 , 12% of the target mapping space is allocated to the target server  104 - 2 , 28% of the target mapping space is allocated to the target server  104 - 3 , 4% of the target mapping space is allocated to the target server  104 - 4 , and 36% of the target mapping space is allocated to the target server  104 - 5 . 
     In some implementations, the target mapping space includes a range of mapping values that are produced by a mapping function. In some implementations, the mapping function is a hash function. A hash function includes any function that maps (variable or fixed length) data (e.g., a string) to a value having a fixed length. For example, the hash function may include the MD5 and the SHA-1 hash functions. 
     In some implementations, a respective target mapping space allocated to (or otherwise associated with) a respective target server includes a contiguous block of mapping values of the target mapping space. For example, if the target mapping space includes 100 mapping values, mapping values 1-20 of the target mapping space are allocated to the target server  104 - 1 , mapping values 21-32 of the target mapping space are allocated to the target server  104 - 2 , mapping values 33-60 of the target mapping space are allocated to the target server  104 - 3 , mapping values 61-64 of the target mapping space are allocated to the target server  104 - 4 , and mapping values 65-100 of the target mapping space are allocated to the target server  104 - 5 . Thus, when the mapping function is applied to at least one parameter of an operation to be performed, the mapping value produced by the mapping function determines to which target server the operation is issued. For example, if the mapping function produces a mapping value of 26 when applied to the at least one parameter of the operation, the operation is issued to the target server  104 - 2 , which has been allocated the mapping values 21-32. 
     In some implementations, when a target server in the set of target servers becomes unavailable, the portion of the target mapping space allocated to (or otherwise associated with) the target server is partitioned between the remaining target servers in the set of target servers proportional to resource capacities of the remaining target servers in the set of target servers. These implementations, are illustrated in  FIG. 2B , which is based on the target mapping space illustrated in  FIG. 2A . In  FIG. 2B , the amount of storage that is available for use on each target server is as follows: 0 for target server  104 - 1 , 24 TB for target server  104 - 2 , 56 TB for target server  104 - 3 , 8 TB for target server  104 - 4 , and 72 TB for target server  104 - 5 . Thus, the total amount of storage that is available for use across the target servers  104 - 1  to  104 - 5  is 150 TB. In some implementations, the target mapping space originally allocated to (or otherwise associated with) the target server  104 - 1  is partitioned between the target servers  104 - 2 ,  104 - 3 ,  104 - 4 , and  104 - 5  as follows: 15% of the target mapping space originally allocated to the target server  104 - 1  is allocated to the target server  104 - 2 , 35% of the target mapping space originally allocated to the target server  104 - 1  is allocated to the target server  104 - 3 , 5% of the target mapping space originally allocated to the target server  104 - 1  is allocated to the target server  104 - 4 , and 45% of the target mapping space originally allocated to the target server  104 - 1  is allocated to the target server  104 - 5 . Continuing the example from above where the target mapping space includes 100 mapping values, the mapping values 1-20 of the target mapping space originally allocated to (or otherwise associated with) the target server  104 - 1  are re-allocated to (or otherwise re-associated with) the target servers  104 - 2 ,  104 - 3 ,  104 - 4 , and  104 - 5  as follows: mapping values 1-3 of the target mapping space are allocated to the target server  104 - 2 , mapping values 4-10 of the target mapping space are allocated to the target server  104 - 3 , mapping value 11 of the target mapping space are allocated to the target server  104 - 4 , and mapping values 12-20 of the target mapping space are allocated to the target server  104 - 5 . Note that in these implementations, the original allocations of the target mapping space allocated to (or otherwise associated with) the target server  104 - 2 ,  104 - 3 ,  104 - 4 , and  104 - 5  remain unchanged. Thus, an operation that was directed to one of these target servers continues to be directed to the same target server. 
     Note that although  FIGS. 2A and 2B  refer to an amount of storage that is available for use by a respective target server, any other resource capacity (or combination of resource capacities) may be used to partition the target mapping space. For example, the resource capacities for the respective target server may include, but are not limited to, an amount of CPU time that is available for use by the respective target server, an amount of memory (e.g., RAM) that is available for use by the respective target server, an amount of network resources of the respective target server (e.g., memory, processing capacity, bandwidth of a network controller for the respective target server) that is available for use by the respective target server, and network resources (e.g., bandwidth) that is available for use by the respective target server (e.g., the network bandwidth of the network links between the respective target server and other computer systems that are available for use). In some implementations, when using a combination of resource capacities to partition the target mapping space, a combining function (e.g., a weighted average, etc.) is used to produce a composite capacity. The composite capacity may then be used to partition the target mapping space (e.g., as discussed above with reference to  FIGS. 2A and 2B ). 
       FIG. 3  is a block diagram  300  illustrating an example process for issuing an operation, according to some implementations. The client computer system  106  issues the operation  330  to the server  102 . Note that although  FIG. 3  illustrates that the operation  330  is received from the client computer system  106 , the operation  330  may be generated by the server  102 . For example, the server  102  may generate the operation  330  in response to other operations being performed on (e.g., processes being executed on) the server  102 . Similarly, the operation  330  may be received from one of the target servers  104 - 1  to  104 -N. 
     An operation processing module  302  of the server  102  receives the operation  330  that was issued by the client computer system  106  and provides the operation  330  to a mapping module  304 . The mapping module  304  applies a mapping function to at least one parameter of the operation  330  to produce a mapping value  332  in a target mapping space  310 . The mapping module  204  uses the mapping value  332  and the target mapping space  310  to identify a target server  334 . In this example, the target server  334  is the target server  104 - 2 . Thus, the operation processing module  302  issues the operation  330  to the target server  104 - 2 . 
       FIG. 4  is a block diagram illustrating the server  102 , according to some implementations. The server  102  typically includes one or more processing units (CPU&#39;s, sometimes called processors)  402  for executing programs (e.g., programs stored in memory  410 ), one or more network or other communications interfaces  404 , memory  410 , and one or more communication buses  409  for interconnecting these components. The communication buses  409  may include circuitry (sometimes called a chipset) that interconnects and controls communications between system components. The server  102  optionally includes (but typically does not include) a user interface  405  comprising a display device  406  and input devices  408  (e.g., keyboard, mouse, touch screen, keypads, etc.). Memory  410  includes high-speed random access memory, such as DRAM, SRAM, DDR RAM or other random access solid state memory devices; and typically includes non-volatile memory, such as one or more magnetic disk storage devices, optical disk storage devices, flash memory devices, or other non-volatile solid state storage devices. Memory  410  optionally includes one or more storage devices remotely located from the CPU(s)  402 . Memory  410 , or alternately the non-volatile memory device(s) within memory  410 , comprises a non-transitory computer readable storage medium. In some implementations, memory  410  or the computer readable storage medium of memory  410  stores the following programs, modules and data structures, or a subset thereof:
         an operating system  412  that includes procedures for handling various basic system services and for performing hardware dependent tasks;   a communication module  414  that is used for connecting the server  102  to other computers via the one or more communication interfaces  404  (wired or wireless) and one or more communication networks, such as the Internet, other wide area networks, local area networks, metropolitan area networks, and so on;   an optional user interface module  416  that receives commands from the user via the input devices  408  and generates user interface objects in the display device  406 ;   the operation processing module  302  that receives operations to be performed and issues the operations to target servers (e.g., the target servers  104 ), as described herein;   the mapping module  304  that applies a mapping function to at least one parameter of an operation to produce a mapping value and identifies a target server based on the mapping value, and that partitions the target mapping space  310  between the target servers, as described herein;   the resource module  306  that obtains and maintains (e.g., updates) resource capacities of the target servers;   the target mapping space  310 , as described herein; and   resource capacities  312  of the target servers, as described herein.       

     In some implementations, the programs or modules identified above correspond to sets of instructions for performing a function described above. The sets of instructions can be executed by one or more processors (e.g., the CPUs  402 ). The above identified modules or programs (i.e., sets of instructions) need not be implemented as separate software programs, procedures or modules, and thus various subsets of these programs or modules may be combined or otherwise re-arranged in various implementations. In some implementations, memory  410  stores a subset of the modules and data structures identified above. Furthermore, memory  410  may store additional modules and data structures not described above. 
     Although  FIG. 4  shows a “server,”  FIG. 4  is intended more as functional description of the various features that may be present in a set of servers than as a structural schematic of the implementations described herein. In practice, and as recognized by those of ordinary skill in the art, items shown separately could be combined and some items could be separated. For example, some items shown separately in  FIG. 4  could be implemented on single servers and single items could be implemented by one or more servers. The actual number of servers used to implement a server and how features are allocated among them will vary from one implementation to another, and may depend in part on the amount of data traffic that the system must handle during peak usage periods as well as during average usage periods. 
       FIG. 5  is a block diagram illustrating the target server  104 - 1 , according to some implementations. Note that following discussion may apply to any target server (e.g., the target servers  104 - 2  to  104 -N). The target server  104 - 1  typically includes one or more processing units (CPU&#39;s, sometimes called processors)  502  for executing programs (e.g., programs stored in memory  510 ), one or more network or other communications interfaces  504 , memory  510 , and one or more communication buses  509  for interconnecting these components. The communication buses  509  may include circuitry (sometimes called a chipset) that interconnects and controls communications between system components. The target server  104 - 1  optionally includes (but typically does not include) a user interface  505  comprising a display device  506  and input devices  508  (e.g., keyboard, mouse, touch screen, keypads, etc.). Memory  510  includes high-speed random access memory, such as DRAM, SRAM, DDR RAM or other random access solid state memory devices; and typically includes non-volatile memory, such as one or more magnetic disk storage devices, optical disk storage devices, flash memory devices, or other non-volatile solid state storage devices. Memory  510  optionally includes one or more storage devices remotely located from the CPU(s)  502 . Memory  510 , or alternately the non-volatile memory device(s) within memory  510 , comprises a non-transitory computer readable storage medium. In some implementations, memory  510  or the computer readable storage medium of memory  510  stores the following programs, modules and data structures, or a subset thereof:
         an operating system  512  that includes procedures for handling various basic system services and for performing hardware dependent tasks;   a communication module  514  that is used for connecting the target server  104 - 1  to other computers via the one or more communication interfaces  504  (wired or wireless) and one or more communication networks, such as the Internet, other wide area networks, local area networks, metropolitan area networks, and so on;   an optional user interface module  516  that receives commands from the user via the input devices  508  and generates user interface objects in the display device  506 ;   the operation processing module  302  that receives operations to be performed and issues the operations to target servers (e.g., the target servers  104 ), as described herein;   the mapping module  304  that applies a mapping function to at least one parameter of an operation to produce a mapping value and identifies a target server based on the mapping value, and that partitions the target mapping space  310  between the target servers, as described herein;   the resource module  306  that obtains and maintains (e.g., updates) resource capacities of the target servers;   the target mapping space  310 , as described herein; and   resource capacities  312  of the target servers, as described herein.       

     In some implementations, the programs or modules identified above correspond to sets of instructions for performing a function described above. The sets of instructions can be executed by one or more processors (e.g., the CPUs  502 ). The above identified modules or programs (i.e., sets of instructions) need not be implemented as separate software programs, procedures or modules, and thus various subsets of these programs or modules may be combined or otherwise re-arranged in various implementations. In some implementations, memory  510  stores a subset of the modules and data structures identified above. Furthermore, memory  510  may store additional modules and data structures not described above. 
     Although  FIG. 5  shows a “target,”  FIG. 5  is intended more as functional description of the various features that may be present in a set of target servers than as a structural schematic of the implementations described herein. In practice, and as recognized by those of ordinary skill in the art, items shown separately could be combined and some items could be separated. For example, some items shown separately in  FIG. 5  could be implemented on single servers and single items could be implemented by one or more servers. The actual number of servers used to implement a target server and how features are allocated among them will vary from one implementation to another, and may depend in part on the amount of data traffic that the system must handle during peak usage periods as well as during average usage periods. 
       FIG. 6  is a block diagram illustrating the client computer system  106 , according to some implementations. The client computer system  106  typically includes one or more processing units (CPU&#39;s, sometimes called processors)  602  for executing programs (e.g., programs stored in memory  610 ), one or more network or other communications interfaces  604 , memory  610 , and one or more communication buses  609  for interconnecting these components. The communication buses  609  may include circuitry (sometimes called a chipset) that interconnects and controls communications between system components. The client computer system  106  includes a user interface  605  comprising a display device  606  and input devices  608  (e.g., keyboard, mouse, touch screen, keypads, etc.). Memory  610  includes high-speed random access memory, such as DRAM, SRAM, DDR RAM or other random access solid state memory devices; and typically includes non-volatile memory, such as one or more magnetic disk storage devices, optical disk storage devices, flash memory devices, or other non-volatile solid state storage devices. Memory  610  optionally includes one or more storage devices remotely located from the CPU(s)  602 . Memory  610 , or alternately the non-volatile memory device(s) within memory  610 , comprises a non-transitory computer readable storage medium. In some implementations, memory  610  or the computer readable storage medium of memory  610  stores the following programs, modules and data structures, or a subset thereof:
         an operating system  612  that includes procedures for handling various basic system services and for performing hardware dependent tasks;   a communication module  614  that is used for connecting the client computer system  106  to other computers via the one or more communication interfaces  604  (wired or wireless) and one or more communication networks, such as the Internet, other wide area networks, local area networks, metropolitan area networks, and so on;   a user interface module  616  that receives commands from the user via the input devices  608  and generates user interface objects in the display device  606 ; and   applications  618  including a web browser  620 .       

     In some implementations, the programs or modules identified above correspond to sets of instructions for performing a function described above. The sets of instructions can be executed by one or more processors (e.g., the CPUs  602 ). The above identified modules or programs (i.e., sets of instructions) need not be implemented as separate software programs, procedures or modules, and thus various subsets of these programs or modules may be combined or otherwise re-arranged in various implementations. In some implementations, memory  610  stores a subset of the modules and data structures identified above. Furthermore, memory  610  may store additional modules and data structures not described above. 
     Although  FIG. 6  shows a “client computer system,”  FIG. 6  is intended more as functional description of the various features which may be present in a client computer system than as a structural schematic of the implementations described herein. In practice, and as recognized by those of ordinary skill in the art, items shown separately could be combined and some items could be separated. 
     Issuing Operations to be Performed 
       FIG. 7  is a flowchart of a method  700  for issuing operations to be performed, according to some implementations. The operation processing module  302  receives ( 702 ) an operation to be performed. In some implementations, the operation processing module  302  receives the operation to be performed from the client computer system  106  (or any other computer system). In some implementations, the operation processing module  302  receives the operation to be performed from a target server (e.g., the target servers  104 - 1  to  104 -N). In some implementations, the operation processing module  302  receives the operation to be performed from a process executing on the server  102 . 
     In some implementations, the operation includes at least one parameter. In some implementations, the operation includes a request to perform a search query and the at least one parameter includes the search query. In some implementations, the operation includes a request to write data to a target server and the at least one parameter includes the data. Note that as discussed above, the operation may include, but are is limited to, an operation to read data stored on a target server, an operation to delete data stored on a target server, an operation to update data stored on a target server, and any operations involving data 
     The mapping module  304  applies ( 704 ) a mapping function to at least one parameter of the operation to produce a mapping value (e.g., the mapping value  332 ) in a target mapping space (e.g., the target mapping space  310 ), where the target mapping space is partitioned between target servers in a set of target servers (e.g., the target server  104 - 1  to  104 -N) proportional to resource capacities of the target servers in the set of target servers (e.g., as described above with reference to  FIG. 2A ). In some implementations, the mapping function is usable to map respective parameters of a respective operation to a respective mapping value in the target mapping space. In some implementations, the mapping function is a hash function (e.g., MD5, SHA-1, etc.). In some implementations, the operation includes a request to perform a search query and the resource capacities of a respective target server include a number of queries per second that the respective target server can process. In some implementations, the operation includes a request to write data to a target server, and the resource capacities of a respective target server include a remaining amount of available storage space on the respective target server. In some implementations, the operation includes a request to read data from a target server and the resource capacities of a respective target server include a number of queries per second that the respective target server can process. In some implementations, the operation includes a request to update data on a target server and the resource capacities of a respective target server include a number of queries per second that the respective target server can process. Operation  704  is described in more detail below with reference to  FIG. 8 . 
     The mapping module  304  identifies ( 706 ) a target server in the set of target servers whose portion of the target mapping space includes the mapping value. 
     The operation processing module  302  issues ( 708 ) the operation to the target server. 
       FIG. 8  is a flowchart of a method for partitioning ( 704 ) a target mapping space, according to some implementations. The resource module  306  obtains ( 802 ) the resource capacities of the target servers in the set of target servers. For example, the resource module  306  may query the target servers to obtain the resource capacities of the target servers. The mapping module  304  then partitions ( 804 ) the target mapping space between the target servers in the set of target servers proportional to resource capacities of the target servers in the set of target servers (e.g., as described above with reference to  FIG. 2A ). 
       FIG. 9  is a flowchart of a method for partitioning a portion of a target mapping space associated with a particular target server, according to some implementations. The resource module  306  determines ( 902 ) that at least one target server in the set of target servers has become unavailable. For example, in response to a query from the resource module  306  to obtain the resource capacities of a particular target server, a response from the particular target server may not be received. In another example, the resource module  306  may determine that a particular target server is scheduled to be taken down at a particular time. In another example, in response to a query from the resource module  306  to obtain the resource capacities of a particular target server, a response from the particular target server may indicate that minimal resource capacities are available on the particular target server (e.g., near zero resource capacities). The mapping module  304  then partitions ( 904 ) the portion of the target mapping space associated with the at least one target server between the remaining target servers in the set of target servers proportional to resource capacities of the remaining target servers in the set of target servers (e.g., as described above with reference to  FIG. 2B ). 
     Note that although the discussion above refers to the operation processing module  302 , the mapping module  304 , and the resource module  306  performing the operations illustrated in  FIGS. 7-9 , these operations may be performed by any module (or modules) of the server  102  or any other computer system (e.g., the target servers  104 - 1  to  104 -N). 
     The methods illustrated in  FIGS. 7-9  may be governed by instructions that are stored in a computer readable storage medium and that are executed by at least one processor of at least one server. Each of the operations shown in  FIGS. 7-9  may correspond to instructions stored in a non-transitory computer memory or computer readable storage medium. In various implementations, the non-transitory computer readable storage medium includes a magnetic or optical disk storage device, solid state storage devices such as Flash memory, or other non-volatile memory device or devices. The computer readable instructions stored on the non-transitory computer readable storage medium may be in source code, assembly language code, object code, or other instruction format that is interpreted and/or executable by one or more processors. 
     Plural instances may be provided for components, operations or structures described herein as a single instance. Finally, boundaries between various components, operations, and data stores are somewhat arbitrary, and particular operations are illustrated in the context of specific illustrative configurations. Other allocations of functionality are envisioned and may fall within the scope of the implementation(s). In general, structures and functionality presented as separate components in the example configurations may be implemented as a combined structure or component. Similarly, structures and functionality presented as a single component may be implemented as separate components. These and other variations, modifications, additions, and improvements fall within the scope of the implementation(s). 
     It will also be understood that, although the terms “first,” “second,” etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first contact could be termed a second contact, and, similarly, a second contact could be termed a first contact, which changing the meaning of the description, so long as all occurrences of the “first contact” are renamed consistently and all occurrences of the second contact are renamed consistently. The first contact and the second contact are both contacts, but they are not the same contact. 
     The terminology used herein is for the purpose of describing particular implementations only and is not intended to be limiting of the claims. As used in the description of the implementations and the appended claims, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the term “and/or” as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     As used herein, the term “if” may be construed to mean “when” or “upon” or “in response to determining” or “in accordance with a determination” or “in response to detecting,” that a stated condition precedent is true, depending on the context. Similarly, the phrase “if it is determined (that a stated condition precedent is true)” or “if (a stated condition precedent is true)” or “when (a stated condition precedent is true)” may be construed to mean “upon determining” or “in response to determining” or “in accordance with a determination” or “upon detecting” or “in response to detecting” that the stated condition precedent is true, depending on the context. 
     The foregoing description included example systems, methods, techniques, instruction sequences, and computing machine program products that embody illustrative implementations. For purposes of explanation, numerous specific details were set forth in order to provide an understanding of various implementations of the inventive subject matter. It will be evident, however, to those skilled in the art that implementations of the inventive subject matter may be practiced without these specific details. In general, well-known instruction instances, protocols, structures and techniques have not been shown in detail. 
     The foregoing description, for purpose of explanation, has been described with reference to specific implementations. However, the illustrative discussions above are not intended to be exhaustive or to limit the implementations to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The implementations were chosen and described in order to best explain the principles and their practical applications, to thereby enable others skilled in the art to best utilize the implementations and various implementations with various modifications as are suited to the particular use contemplated.