Abstract:
Methods for parallel query execution of a database operation on a database utilizing a graphics processing unit (GPU) are presented including: receiving query by a host, the query including database relations; starting a GPU kernel, where the GPU kernels include a GPU memory; hash partitioning the database relations by the GPU kernel; loading the partitioned database relations into the GPU memory; loading keyed partitions corresponding the hash partitioned database relations into the GPU memory; building a hash table for a smaller of the hash partitioned database relations; and executing the query. In some embodiments, methods further include returning a result of the query. In some embodiments, methods further include when the query is a long query including a number of operators, parsing the long query into a number of sub-queries; for each of the sub-queries, starting one of the GPU kernels such that the sub-queries are processed in parallel.

Description:
BACKGROUND 
     Traditional database systems execute database queries on disk-based tables. Research has shown that traditional disk-based database query execution often suffers from high penalties arising from, for example, memory latencies, processors waiting for data to be fetched from the memory, and L 1  data and L 2  instruction stalls. Therefore, to tackle this problem, multiprocessors are being increasingly utilized for executing database queries. Complementary to the disk-based tables are the in-memory tables. In-memory tables are faster than disk-based tables because the fetching from and loading to the disk component is eliminated. In-memory enabled systems can therefore use more efficient techniques to provide maximum performance. 
     A Graphics Processing Unit (GPU) is a massively parallel piece of hardware which can be thought of as several processors with its own local memory. A GPU may operate as an independent co-processor within the host computer. Back in the late nineties, the games industry provided the necessary impetus for the development of the GPU for accelerating graphics in games. Recently, architectures have been configured to support programmability. That is, general-purpose programs may be written to run on the GPU. GPU enabled programs are well suited to problems that involve data-parallel computations where the same program is executed on different data with high arithmetic intensity. 
     As such, GPU enabled database systems are presented herein. 
     BRIEF SUMMARY 
     The following presents a simplified summary of some embodiments of the invention in order to provide a basic understanding of the invention. This summary is not an extensive overview of the invention. It is not intended to identify key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some embodiments of the invention in a simplified form as a prelude to the more detailed description that is presented below. 
     As such, methods for parallel query execution of a database operation on a database utilizing a graphics processing unit (GPU) are presented including: receiving query by a host, the query including database relations; starting a GPU kernel, where the GPU kernels include a GPU memory; hash partitioning the database relations by the GPU kernel; loading the partitioned database relations into the GPU memory; loading keyed partitions corresponding the hash partitioned database relations into the GPU memory; building a hash table for a smaller of the hash partitioned database relations; and executing the query. In some embodiments, methods further include returning a result of the query. In some embodiments, methods further include when the query is a long query including a number of operators, parsing the long query into a number of sub-queries; for each of the sub-queries, starting one of the GPU kernels such that the sub-queries are processed in parallel; and returning to the hash partitioning. In some embodiments, the host is a CPU, and database data and database keys are stored on the GPU memory. In some embodiments, the host is a CPU, database data and first database keys are stored on a disk data store, and second database keys are stored on the GPU memory. In some embodiments, methods further include synchronizing the first database keys with the second database keys. In some embodiments, the host is a database node, first database data and first database keys are stored on a disk data store, and second database data second database keys are stored on the GPU memory. 
     In other embodiments, computing device program products for parallel query execution of a database operation on a database utilizing a graphics processing unit (GPU) in coordination with a computing device are presented including: a computer readable medium; first programmatic instructions for receiving query by a host, the query including database relations; second programmatic instructions for starting a GPU kernel, where the GPU kernels include a GPU memory; third programmatic instructions for hash partitioning the database relations by the GPU kernel; fourth programmatic instructions for loading the hash partitioned database relations into the GPU memory; fifth programmatic instructions for loading keyed partitions corresponding the hash partitioned database relations into the GPU memory; sixth programmatic instructions for building a hash table for a smaller of the hash partitioned database relations; seventh programmatic instructions for executing the query; and eighth programmatic instructions for returning a result of the query, where the programmatic instruction are stored on the computer readable storage medium. 
     In other embodiments, GPU enabled database systems for parallel query execution are presented including: a database; a GPU in communication with the database, where the GPU is configured for processing a database query, where the GPU includes at least one GPU kernel, the at least GPU kernel including GPU memory, and where the GPU is configured for parallel processing the database query; and a host for receiving database queries. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which: 
         FIG. 1  is an illustrative representation of a G80 Architecture compliant GPU in accordance with embodiments of the present invention; 
         FIG. 2  is an illustrative representation of a memory hierarchy on a GPU in accordance with embodiments of the present invention; 
         FIG. 3  is an illustrative representation of a coalesced memory pattern and a non-coalesced memory pattern in accordance with embodiments of the present invention; 
         FIG. 4  is an illustrative flowchart of methods for providing GPU enabled database services in accordance with embodiments of the present invention; 
         FIG. 5  is an illustrative representation of a full GPU enabled database system utilizing in-memory tables in accordance with embodiments of the present invention; 
         FIG. 6  is an illustrative representation of a scratch pad for a GPU enabled database system in accordance with embodiments of the present invention; and 
         FIG. 7  is an illustrative representation of a full GPU enabled database system utilizing disk based tables in accordance with embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     As will be appreciated by one skilled in the art, the present invention may be embodied as a system, method or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system.” Furthermore, the present invention may take the form of a computer program product embodied in any tangible medium of expression having computer usable program code embodied in the medium. Any combination of one or more computer usable or computer readable medium(s) may be utilized. The computer-usable or computer-readable medium may be, for example but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium. More specific examples (a non-exhaustive list) of the computer-readable medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CDROM), an optical storage device, a transmission media such as those supporting the Internet or an intranet, or a magnetic storage device. Note that the computer-usable or computer-readable medium could even be paper or another suitable medium upon which the program is printed, as the program can be electronically captured, via, for instance, optical scanning of the paper or other medium, then compiled, interpreted, or otherwise processed in a suitable manner, if necessary, and then stored in a computer memory. In the context of this document, a computer-usable or computer-readable medium may be any medium that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The computer-usable medium may include a propagated data signal with the computer-usable program code embodied therewith, either in baseband or as part of a carrier wave. The computer usable program code may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF, etc. 
     Computer program code for carrying out operations of the present invention may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, Smalltalk, C++ or the like and conventional procedural programming languages, such as the “C” programming language or similar programming languages. The program code may execute entirely on the user&#39;s computer, partly on the user&#39;s computer, as a stand-alone software package, partly on the user&#39;s computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user&#39;s computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider). 
     The present invention is described below with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. 
     These computer program instructions may also be stored in a computer-readable medium that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable medium produce an article of manufacture including instruction means which implement the function/act specified in the flowchart and/or block diagram block or blocks. 
     The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide processes for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks 
     Referring now to the Figures, the flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions. 
     Compute Unified Device Architecture (CUDA™) is a toolkit that allows general purpose programs written in a C-like language to be executed. CUDA™ toolkit exposes the underlying target hardware via a C-like API. CUDA™ is designed to increase performance in many data parallel applications by supporting execution of thousands of threads in parallel. As such, a compiled CUDA™ program may scale with the advances in hardware. There are at least two ways a GPU-enabled database may be implemented—a) in one embodiment, a full-fledged database system may be enabled, and b) a scratch pad for accelerating other database queries may be enabled, that is, a GPU-memory database for just executing database queries may be enabled. 
       FIG. 1  is an illustrative representation  100  of a G80 Architecture compliant graphics processing unit (GPU) in accordance with embodiments of the present invention. As illustrated, a G80 Architecture may include a number of components including: a host  102 , a input assembler  104 , a thread execution manager  106 , a load/store  108 , and a global memory  110 . These components function in concert with a number of shared multiprocessors  120 . A typical G80 Architecture compliant GPU may contain 128 stream processors  122  divided into 8 shared multiprocessors  120 , each containing 16 streaming processors. Each shared multiprocessor  120  contains local shared memo  124  which is shared by the threads running on the shared multiprocessor. This is advantageous because it helps in coalesced access—when groups of threads operate on nearby data. 
       FIG. 2  is an illustrative representation of a memory hierarchy  200  on a GPU in accordance with embodiments of the present invention. Memory hierarchy  200  includes per-thread memory  204 , per-thread group memory  208 , and global/device memory  210 . Global/device memory  210  is accessible by any thread running on the GPU. Reads and writes to and from device memory  210  are slow as compared to other memories  204  and  208 . GPU threads  208  are extremely light-weight as compared to CPU threads and hence there is essentially zero overhead in the creation of thousands of threads. Notably, threads are not run individually on a processor. Rather multiple threads are run in thread groups  206  called warps which are executed on a single shared multiprocessor (see  FIG. 1 ,  120 ). Threads in a warp can share the memory local to the shared multiprocessor. This ability leads to an increase in performance because fewer reads/writes are made to the global memory to fetch and load data. That is, data is fetched once into a shared memory of the shared multiprocessor; computations are performed; and results are uploaded to the global memory. 
     Embodiments described herein optimize memory utilization by a) utilizing parallelism effectively and efficiently, and b) coalescing reads from global memory. In utilizing parallelism effectively, parallel execution of database operations are executed over as many threads as possible at any given time on a GPU. In coalescing reads from global memory, contiguous regions of global memory may be operated upon by threads in a thread group.  FIG. 3  is an illustrative representation of a coalesced memory pattern  300  and a non-coalesced memory pattern  310  in accordance with embodiments of the present invention. In coalesced memory pattern  300 , threads t 0  to t 3   302  are resident in order in memory  304 . In contrast in non-coalesced memory pattern  310 , threads t 0  to t 3   312  are resident out of order in memory  314 . Coalesced memory patterns may provide processing efficiencies in some embodiments described herein. In some embodiments, hash partitioned relations may be loaded into GPU memory in a coalesced access pattern such that a contiguous region of GPU memory is utilized. 
       FIG. 4  is an illustrative flowchart  400  of methods for providing GPU enabled database services in accordance with embodiments of the present invention. In particular, methods for parallel query execution of a database operation on a datable utilizing a GPU are illustrated. At a first step  402 , the method receives a query. Queries may be received by a host in any manner known in the art without departing from the present invention. In embodiments, a query may include at least two database relations. At a next step  404 , the method determines whether the received query is a long query. In embodiments, a long query may require additional processing steps. If the method determines at a step  404  that the query is not a long query, the method continues to a step  406  to start a GPU kernel whereupon the method continues to a step  410 . If the method determines at a step  404  that the query is a long query, the method continues to a step  420  to parse the long query into a number of sub-queries. Partitioning long queries provides an advantage of executing queries in parallel across several GPU kernels. As such, at a next step  422 , the method starts a GPU kernel for each sub-query. Sub-queries may be determined based on a variety of parameters in embodiments including, for example, size. That is, a sub-query may be determined based on whether the sub-query will fit into GPU memory. 
     The method continues to a step  410  to hash partition all relations by GPU kernel(s). Hash partitioning may be accomplished utilizing in any manner known in the art without departing from the present invention. At a next step  412 , the method loads hashed partition relations and keys into GPU memory. At a next step  414 , the method builds a hash table for the smaller table and, at a step  416 , executes the query or sub-queries by GPU kernel(s). Results returned at a step  416  may be written first to GPU device memory and then host memory accessible by a user whereupon the method ends. 
     In one example embodiment, consider a case of a JOIN between two database relations R and S. Assume the relations are small-enough to fit into the GPU memory. Thus, the example is not a large query. Embodiments then hash partition both relations (R and S) and bring in the same keyed partition from both relations into GPU memory. Embodiments then build a hash table for the smaller table and probe the other relation for matches. In one embodiment, hash is performed on the join key. If relations are bigger than the available GPU memory, multiple hash functions may be utilized to reduce the size. In a case of a long query embodiment with many operators, the long query may be partitioned the query into several sub-queries that may be executed in parallel and then combined after processing. 
     It may be appreciated that at least some in-memory issues associated with GPU enabled database processing such as: table choice, concurrency, data volatility, and memory consumption. In embodiments utilizing CEILADB™, table choice may be tied to number of accesses/second made to the table. In further embodiments utilizing CEILADB™, concurrency may be compromised because thread blocks may be working in a same shared multiprocessor. As such, in embodiments, a call such as SYNCTHREADS (from a CUDA™ Library) will synchronize the threads in the same shared multiprocessor. However, any similar call may be made without departing from embodiments disclosed herein. If two threads from two different shared multiprocessors want to write data, they must synchronize through the global memory. In further embodiments utilizing CEILADB™, volatility may be solved by implementing a function that will store the data from the GPU to the disk. In further embodiments utilizing CEILADB™, memory consumption may be solved by enabling a user, at any time, to query the amount of memory being used by the tables created by the user. The user can also set memory consumption parameters which control the way data is written to memory or to disk—every time or when the used memory. 
     The following examples are provided for clarity in understanding embodiments of the present invention and should not be construed as limiting.  FIG. 5  is an illustrative representation of a full GPU enabled database system  500  utilizing in-memory tables in accordance with embodiments of the present invention. In the illustrated embodiment, a user  502  may log on to host  504  either locally or remotely to make queries. In some embodiments, the host is a CPU. In some embodiments, queries are SQL-type queries. Queries may be sent to GPU  506 , executed on GPU  506 , and returned to host  504 . Results may then be returned to user  502 . As noted above, in embodiments, a GPU may be a G80 architecture compliant GPU. As illustrated, GPU  506  may be configured to utilize in-memory tables. As such, in embodiments, database data and database keys may be stored on the GPU memory, which memory may be shared in some embodiments. Because database data and database keys reside entirely in GPU memory, performance advantages may be achieved. However, due to the limited size of GPU memory, limitations in database table size may be required in embodiments. As noted above, in embodiments utilizing CEILADB™ memory consumption may be solved by enabling a user, at any time, to query the amount of memory being used by the tables created by the user. The user can also set memory consumption parameters which control the way data is written to memory or to disk—every time or when the used memory. 
       FIG. 6  is an illustrative representation of a scratch pad for a GPU enabled database system  600  in accordance with embodiments of the present invention. In the illustrated embodiment, a user  602  may log on to host  604  either locally or remotely to make queries. In some embodiments, the host is a database node. In some embodiments, queries are SQL-type queries. Queries may be sent to GPU  606 , executed on GPU  606 , and returned to host  604 . Results may then be returned to user  602 . As noted above, in embodiments, a GPU may be a G80 architecture compliant GPU. In this embodiment, a user may exploit the high computational power and memory bandwidth of the GPU for accelerating database queries of other database systems since the host, in this example, is a database node. As above, in embodiments, database data and database keys may be stored on the GPU memory, which memory may be shared in some embodiments. In addition, in embodiments, database data and database keys may be stored on the tertiary disks  608 . In embodiments, in making queries to a commercial database, user  602  is unaware that queries are processed by GPU  606 . 
       FIG. 7  is an illustrative representation of a full GPU enabled database system  700  utilizing disk based tables in accordance with embodiments of the present invention. In the illustrated embodiment, a user  702  may log on to host  704  either locally or remotely to make queries. In some embodiments, the host is a CPU. In some embodiments, queries are SQL-type queries. Queries may be sent to GPU  706 , executed on GPU  706 , and returned to host  704 . Results may then be returned to user  702 . As noted above, in embodiments, a GPU may be a G80 architecture compliant GPU. In this embodiment, when a user is dealing with huge volumes of data, it may not be possible to store all the data in the GPU memory. Hence, in embodiments, database data and database keys may be stored on tertiary disks  708 . In addition, in embodiments, database keys may be stored on GPU memory. As such, a host copy will be used when fetching data from the disks and GPU device copy will be used to access tuples in GPU memory. After insert operations to a database all copies must by synched to avoid inconsistencies. In some embodiments, it is imperative to pipeline the disk accesses with computations in order to achieve significant performance increases. 
     While this invention has been described in terms of several embodiments, there are alterations, permutations, and equivalents, which fall within the scope of this invention. It should also be noted that there are many alternative ways of implementing the methods, computer program products, and apparatuses of the present invention. Furthermore, unless explicitly stated, any method embodiments described herein are not constrained to a particular order or sequence. Further, the Abstract is provided herein for convenience and should not be employed to construe or limit the overall invention, which is expressed in the claims. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations, and equivalents as fall within the true spirit and scope of the present invention.