Abstract:
A method, system and process for enhancing a database server by improving dynamic memory allocation and memory copying during the process of reconstructing a data structure from a communication buffer.

Description:
FIELD OF THE INVENTION 
     The invention generally relates to improvements in database processing and more particularly to dynamic buffering to enhance remote access to a database. 
     BACKGROUND OF THE INVENTION 
     System management of remote access to a database is the subject of numerous articles and patents. For example, U.S. Pat. No. 5,014,221 discloses a print server with arbitrated client access, U.S. Pat. No. 4,511,964 discloses dynamic memory mapping for a memory controller that serves to effectuate the allocation, extension and deallocation of dynamic structures, and U.S. Pat. No. 5,025,491 discloses a communication network with associated server stations and server addresses resolved by a computer algorithm. However, none of the prior art references that applicant is aware of discloses the enhanced database server of the subject invention. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is a primary objective of the present invention to provide dynamic buffering to enhance a database server. 
     These and other objectives of the present invention are accomplished by constructing a data structure in a memory on a first computer for use in accessing information from a database on a second computer by calculating a memory requirement data structure from data structures generated by a processor in the first computer and constructing a communication buffer. The communication buffer contains the memory requirement data structure and information from the database including the contents of the data structure. 
     The dynamic buffer refers to the ability to handle data structure information that will not fit in a single communication buffer. Thus, if a single communication buffer will not accommodate the transmission, then additional communication buffers are constructed containing additional information. The communication buffers are transmitted to a second computer where they are received and parsed to determine the memory necessary on the second computer to accommodate the data structure in the one or more communication buffers. Thereafter, the second computer allocates a contiguous memory if the database information can not fit into one communication buffer and dynamically adjusts the location of the communication buffer so that database information will be received directly into the contiguous memory allocated in without additional memory copying overhead. 
     If the memory requirements are more than the size of the communication buffer, the server allocates a buffer which can accommodate the entire data structure. Instead of copying the communication buffer into the buffer, pointers are assigned to the address of the buffer allocated for the data structure. Then the pointers are dynamically adjusted so that data is received directly into the buffer. After all data has been received, the server adjusts pointers in the buffer to reconstruct the engine data structure back. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of a personal computer system in accordance with the subject invention; and 
     FIG. 2 is an example of the system control flow of a remote database request in accordance with the subject invention; 
     FIG. 3 is a flowchart setting forth the detailed logic in accordance with the subject invention; 
     FIG. 4 is a diagram of a data structure in accordance with the subject invention; 
     FIG. 5 is a flowchart of a data structure reconstruction routine of the server in accordance with the subject invention; and 
     FIG. 6 is an example of a dynamic buffer logic in accordance with the subject invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention is preferably practiced in the context of an operating system resident on an IBM PS/2 computer available from IBM Corporation. A representative hardware environment is depicted in FIG. 1, which illustrates a typical hardware configuration of a workstation in accordance with the subject invention having a central processing unit 10, such as a conventional microprocessor, and a number of other units interconnected via a system bus 12. The workstation shown in FIG. 1 includes a Random Access Memory (RAM) 14, Read Only Memory (ROM) 16, an I/O adapter 18 for connecting peripheral devices such as disk units 20 to the bus, a user interface adapter 22 for connecting a keyboard 24, a mouse 26, a speaker 28, a microphone 32, and/or other user interface devices such as a touch screen device (not shown) to the bus, a communication adapter 34 for connecting the workstation to a data processing network and a display adapter 36 for connecting the bus to a display device 38. The workstation has resident thereon the OS/2 operating system and the computer software making up this invention which is included as a toolkit. 
     A private protocol was implemented in IBM&#39;s OS/2 1.3 Extended Edition (EE) operating system to provide remote access to a relational database. The protocol is discussed in detail in two IBM publications, 1. Distributed Relational Database Architecture Reference, August 1990, IBM, SC26-4651; and 2. Distributed Data Management (DDM) Architecture Reference, August 1990, IBM, SC21-9526. Performance tests uncovered a problem with the memory allocation and memory copying during the process of reconstructing the database data structures. 
     The invention discloses an efficient design for server memory allocation for a remote protocol. The protocol is designed for OS/2 Extended Services (ES) 1.0 Remote Database Service. The system uses a communication buffer without allocating extra storage for reconstructing data structures. It reduces memory requirement for the server, and reduces the cost of memory copying. 
     Compared with the previous design in OS/2 1.3 Extended Edition (EE), the current remote protocol achieves up to 56 percent speedup in throughput and 36 percent speedup in end user response time. The design of SQLJRA remote protocol leverages data structures built on either the client or the server in a homogeneous environment that are similarly structured. Therefore, the underlying data structures are passed directly, without the conversion step being necessary. 
     On the client, a data stream constructor builds a data stream from the data structures. If the data structure contains a pointer, the actual data pointed to by those pointers will be placed in the data stream. The data structure reconstructor on the server builds the data structures according to the data string received from the client. In order to rebuild the engine data structures on the server, the server needs to allocate memory for the data structures. The invention addresses the problem of how to allocate memory efficiently to reconstruct the data structures. 
     In OS/2 ES 1.0 database manager, each client and server has its own communication buffer to store the information sent and received. The size of the communication buffer is determined by the block size in the database configuration file. The minimum size of the communication buffer is 4K. The requestor will put data in the communication buffer and invoke communication routines to actually send the data. The server receives data from its own communication buffer. 
     Before the client puts the engine data structures into the communication buffer, the client must first calculate the total memory required by the database data structures. The database data structures include the JRA control structure, input SQLDA, output SQLDA and SQLCA. The memory requirement information will be put into the communication buffer. Then, the client copies the control structures into the communication buffer. If the communication buffer is filled up, the client calls the communication routines to send the buffer to the server. 
     The server, then, calls communication routines to receive data. The data sent by the client will be in server&#39;s communication buffer. Since the client put the memory requirement information into its communication buffer first, the server will receive it in the first buffer received. The server will then use this information to allocate memory for data structures. 
     Let the memory needed by the engine data structure be M, the size of the communication buffer be B and size of a segment be S. A segment is the maximum virtual memory that can be allocated for each memory allocation call. For example, a maximum segment size for 16 bit OS/2 is 64K. First, if the memory needed by the engine data structure (M) is less than the size of the communication buffer (B), then NO extra memory is needed. Since we passed these data structures in their native form, we can make use of the communication buffer to rebuild the engine data structure back. The client simply locates the starting position of each data structure, and assigns a new address to the pointer fields in the SQLJRA. 
     FIG. 2 illustrates a sample flow of information for remote database requests. First, the database runtime API routines 200 prepare database engine data structures 202 from user&#39;s SQL request. These data structures include SQLRA 202 (SQL Request Area) and SQLDA 202 (SQL Data Area). Then, the Gateway mapper 210 maps SQLRA to SQLJRA (Gateway Interface Request Area). The data structures (SQLJRA and SQLDA) 214 are given to the SQLJRA data stream constructor. Then, the SQLJRA data stream constructor 220 calculates the memory requirement for the data stream 222. 
     The information about the memory requirement will be put into a data structure (SQLCPLEN) which will be described later. SQLJRA data stream constructor will also construct a data stream 222 from the data structures and put the data stream into the communication buffer 230. The database manager transport routines 240/250 transmit the communication buffer to the server through transport layer communication protocol. 
     On the server side, the database manager 280 transport routines receives the data stream into a communication buffer. The first thing that the SQLURA data structure constructor 260 gets from the communication buffer is the memory requirement data structure. With the information in the memory requirement data structure, the server calculates what is the total memory requirement to reconstruct the data structure. The data structure constructor allocates appropriate memory size, receives data from the data stream into the allocated memory and rebuilds the data structure. 
     The reconstructed data structure is given to the gateway router 270 which maps the SQLJRA gateway interface structure into SQLRA which is the data structure that the database actually employs. The SQLRA and SQLDA are given to the database 280 to perform the SQL request. 
     FIG. 3 is the detailed flowchart of SQLJRA data stream constructor on the client. As mentioned above, the data stream constructor needs to prepare a data structure which contains the memory requirement information needed by the server. Processing commences at function block 300 where a location pointer is initialized to the first available record in the communication buffer. Then, in function block 310, the current buffer location pointer is assigned to SQLCPLEN, the length of the two data structures are calculated in function block 320, and total input and output data lengths are assigned to the appropriate variables as shown in function blocks 330 and 340. Then, the number of variables for input and output are calculated and placed in the communication buffer as shown in function block 350 and 360. Finally in function blocks 370, 380 and 390 the length of each variable in the communication buffer are recorded and an exit is performed at terminal 392. 
     DATA STRUCTURE IN ACCORDANCE WITH THE SUBJECT INVENTION 
     The following is the control structure that the client passes to the server to indicate the memory and data length information. 
     
         ______________________________________  struct sqlcplen   {    .sup. unsigned long cs.sub.-- len;    .sup. unsigned long in.sub.-- data.sub.-- len;    .sup. unsigned long out.sub.-- data.sub.-- len;    .sup. unsigned long num.sub.-- of.sub.-- vars;    .sup. unsigned long num.sub.-- of.sub.-- out.sub.-- vars;    .sup. unsigned long sqlvar.sub.-- len 1!;   };______________________________________ 
    
     An intuitive approach to building this data structure is to define a structure, to assign values in the structure and then move it into the communication buffer. Instead, a control structure is built in the communication buffer and values are stored in the appropriate control structures. In this case, it is not necessary to copy the control structure into the data stream. 
     CS --  LEN is the total length of the control structures which include SQLJRA and SQLCPLEN. The server uses this information to locate the end of the control structure. 
     IN --  DATA --  LEN is the length of user input data area. 
     OUT --  DATA --  LEN is the length of the user output data area. 
     IN --DATA   --  LEN and OUT --  DATA --  LEN are used not only for calculating the total memory space needed for data structures but also used for calculating number of segments needed for user input and output data area. 
     NUM --  OF --  VARS is the number of input and output sqlvars. The value of NUM --  OF --  VARS is passed from SQLD in the user input SQLDA. 
     NUM --  OF --  OUT --  VARS is the number of output sqlvars. The value of NUM --  OF --  OUT --  VARS is passed from SQLD in the user output SQLDA. 
     SQLVAR --  LEN is an array to store the actual data length of each sqlvar. Each SQLVAR in the user&#39;s input SQLDA be inspected to get the actual data length. The server uses the NUM --  OF --  VARS to calculate the input SQLDA length (IN --  DA --  LEN) and use NUM --  OF --  OUT --  VARS to calculate the output SQLDA length (OUT --  DA --  LEN). 
     As can be seen from FIG. 4, the SQLJRA data structure 401 consists of 2 general parts, header information and a set of parameters. The header information 400, 410, 420, 430, 440, and 450 describes the SQLJRA data structure and the type of request. Each parameter 460 is a triplet consisting of a length, a type and a pointer. This step moves data pointed to by the parameter pointer into the communication buffer containing the communication data stream. The intuitive way to implement this function is to deference parameter pointer one at a time and put the data into the data stream. Since each triplet has the same structure, it is more efficient to have a loop for dereferencing the triplet pointers. 
     A triplet structure is defined and cast as the first SQLJRA triplet address with a pointer to this triplet structure, and then the triplet pointer is employed to access each SQLJRA parameters. 
     Fourth, the client moves input and output SQLDA into the data stream. Finally, the client loops through user input SQLDA and puts the input data into the data stream. Since each sqlvar has the same structure, the same technique that we use for SQLJRA triplet is applied here. 
     FIG. 5 is the detail flowchart of the data structure reconstructor on the server. The first thing that the data structure reconstructor gets from the communication buffer is the data length control structure as shown in function block 500. With this information, the server calculates total memory space needed (M) for data structures as shown in function block 510. First of all, if the memory needed by the data structure (M) is determined to be less than the size of the communication buffer (B) in decision block 520, then NO extra memory is needed. Since SQLJRA remote protocol passed these data structures in its native forms, the communication buffer is used to rebuild the data structure as shown in function block 522. The client just locates the starting position of each data structure, and assign the new address to the pointer fields in the SQLJRA as shown in function block 524 and exits via terminal 526. 
     If the memory necessary is larger than one communication buffer as detected in decision block 520, then, the server allocates a buffer which can accommodate the data structure as shown in function block 530. If the location of the buffer is B, the size of the communication buffer is C, and the location of the communication buffer is L, then the number of receives that the server invokes is i. 
     First, the server copies the contents of the communication buffer into the server buffer as shown in function block 540. After the copying, the server dynamically adjusts the address of the communication buffer according to the following formula as shown in function blocks 550 and 560: 
     
         L=(B+(i-1)*C)·2 
    
     Two is subtracted from L because SNA requires the first two bytes of the communication buffer to be the actual data length received by the server. Before the receive, the server needs to save the last two bytes of the communication buffer and to restore it back after the receive is finished. All data will be received into the server buffer in order as shown in function block 560. After all the data is received, the server will locate the starting position of data structures and assign pointers in the SQLJRA control structure as shown in function block 524. 
     FIG. 6 is an example of data structure reconstruction in accordance with the subject invention. L1 602 is the communication buffer 600 address for the second receive, L2 603 is the communication buffer address for the third receive and L3 604 is the communication buffer address for the fourth receive. After all data is received by the server in the server buffer 610, the server adjusts pointers in the data structure 620. ##SPC1## 
     While the invention has been described in terms of a preferred embodiment in a specific system environment, those skilled in the art recognize that the invention can be practiced, with modification, in other and different hardware and software environments within the spirit and scope of the appended claims.