JP2000048028A - Method for acquiring record of database - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten waiting time for a user program by dynamically changing the number of records to be acquired from a server or the number of recordes allowed to be stored by a client in a data base access system in a distributed environment. SOLUTION: A memory monitoring object 21 in a client 20 determines the maximum number of recordes to be stored in a memory in accordance with free memory quantity. A data acquiring object 22 determines the number of records to be acquired next from acquisition speed and the number of records acquired in past data acquisition and acquires data from a server 30.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD OF THE INVENTION

[0002]

2. Description of the Related Art In a client / server type database search system in which data is processed using a database, all records are stored in the client memory at once due to memory limitations depending on the amount of data to be obtained. Therefore, all records are acquired by determining the number of records to be acquired at once to an appropriate value, dividing the data into one block, and acquiring the data in blocks.

In such a case, if the user issues a request to acquire the next block after the processing of one block is completed, the user will have to wait while acquiring the next block. The waiting time of the user can be reduced by pre-reading the next block in the client memory in advance.

[0004]

In the above prior art,
Because the load on the client machine and network is not taken into account and the record is always read ahead in block units, even when there is room in the client memory,
Even when only one block is read ahead, or when there is not enough time to read ahead in the client memory, even if the processing speed is drastically reduced due to swapping while trying to prefetch, or even if the network is overloaded, one block worth There have been problems in terms of efficiency and performance, such as taking a long time to acquire records in an attempt to acquire them, and acquiring only one record at a time depending on the database management system (hereinafter referred to as DBMS).

An object of the present invention is to divide a user's database search process into a machine (server machine) for searching a database in a distributed environment and a machine (client machine) used by a user for data processing. By pre-reading the records from the database in advance, the client machine acquires the data from the server so that the client communication is not restricted by the DBMS, which is a limitation on the number of records acquired at a time, and is stored in the client memory. Instead of reading records in blocks, the number of records to be read is dynamically changed according to changes in the load on the client or network or the processing speed of records by the user. The maximum that can be held By dynamically changing the number of codes, as intended for the acquisition of the records efficiently.

[0006]

An object of the present invention is to provide an apparatus for reading records from a database in a memory on a server machine in advance, and a record which can be read into a memory of a client machine in accordance with an available memory space on a client machine. This is achieved by providing a device that determines the maximum number of records and a device that determines the number of records that the client will acquire from the server next time from the number and speed of records in the past data acquisition.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows the relationship between objects constituting the system and the flow of data, and a basic processing method of the entire system will be described.

In the server machine 30, the memory monitoring object (server side) 32 determines the maximum number of records held in the server memory 31, and the database retrieval object 33 repeatedly acquires data from the database 40 until the maximum number is satisfied. Since the maximum number of records held depends on the free space in the memory, the maximum number of records is recalculated every time data is acquired from the database 40.

In the client machine 20, the memory monitoring object (client side) 21 determines the maximum number of records held in the client memory 24, and repeatedly issues an acquisition command to the data acquisition object 22 until the maximum number is satisfied. This is also similar to the processing of the server machine 30,
Each time data is acquired from the server machine 30, the maximum number of records held is recalculated. When receiving the acquisition command, the data acquisition object 22 calculates the number of acquisitions this time from the number of acquisitions at the time of the previous acquisition and the time required for acquisition, and acquires data from the server.

The database access interface 23
Provides an interface to the user program 10 for executing a database search and obtaining a search result.

Next, the processing flow in the server is shown in FIG.
This will be described with reference to the flowchart shown in FIG. First, the memory usage of the entire machine in the server memory is calculated (101). Next, it is checked whether the memory usage is within the allowable range (102). If the memory usage is within the allowable range, it is checked whether or not the current memory usage exceeds the allowable range by adding the memory amount required for acquiring records from the database to the current memory usage (10).
3). If it is within the allowable range, a record is obtained from the database (104). Then, it is checked whether all records of the search result have been obtained from the database (105). If all of them have been acquired, the process ends (END). If you have not yet obtained all (10
Return to 1) and continue the process.

If the memory usage exceeds the allowable range in (103), it is checked whether the number of records currently held in the server memory is below the lower limit of the number of records held by the user specified by the user (106). If it is lower, the process goes to (104) to continue the process. If the number of held records exceeds the lower limit in (106), the process returns to (101) without acquiring records from the database.

If the memory usage exceeds the allowable range in step (102), the number of records of the database currently stored in the server memory is checked (106), and this is below the lower limit of the number of records held by the user specified by the user. If yes, get record from database (104)
If the number of records held by the server exceeds the lower limit, the process returns to (101).

FIG. 3 shows a flowchart of the memory monitoring object of the client, which will be described.
First, the memory usage of the entire machine in the client machine is calculated (201). Next, it is checked whether the memory usage is within the allowable range (202). If the memory usage is within the allowable range, add the amount of memory required to acquire data from the server (specified by the data acquisition object) to the current memory usage and check whether it exceeds the allowable range (203). If it is within the allowable range, a record acquisition request is issued to the data acquisition object (204). Thereafter, it is checked whether all records have been acquired from the server (205). If all of them have been acquired, the processing ends (END). If all records have not been acquired yet, the process returns to (201).

If the memory usage exceeds the allowable range in (203), it is checked whether or not the number of records of the database currently held in the client memory is below the lower limit of the number of records held by the user specified by the user (206). If this is below the threshold, a record acquisition request is issued to the data acquisition object (204), and it is checked whether all records have been acquired from the server (2).
05), if all have been acquired, end (END); otherwise, return to (201). If not less than (206), no record is obtained from the server (20
Return to 1).

If the memory usage exceeds the allowable range in (202), the number of records of the database currently held in the client memory is checked (206). If this is less than the lower limit of the number of client owned records specified by the user, a record acquisition request is issued to the data acquisition object (204). If the number exceeds the lower limit of the number of records held by the client, the process returns to (201) without acquiring a record from the server.

FIG. 4 shows a flowchart of the data acquisition object of the client, and the description will be made along this flowchart.
A request is issued from the server to acquire an Nreq record (301). The value of Nreq has already been obtained by calculation at the time of the previous record acquisition. After the acquisition is completed, a record acquisition speed V (= N / T) is calculated from the number N of acquisitions and the time T required for acquisition (302). Then, the value Vmax, which is the fastest acquisition speed, is compared with V (303). V
Is faster, the value of Vmax is updated with V (30
4).

Further, the number of acquisitions Nmax obtained when the acquisition speed is the fastest is compared with N (305). Thereafter, the value of Nmax is updated with N (306, 308). (30
As a result of the comparison in 5), when N is larger than Nmax,
The value of the next acquisition number Nreq is set to be larger than N (30
7). If the result of (305) is that N is smaller than Nmax, the value of Nreq is made smaller than N (309). In both cases, the process ends (END).

If the result of the comparison in (303) shows that V is slower, Nmax is compared with N (310). As a result of the comparison, when N is larger than Nmax, the value of Nreq is set to “N
max <Nreq <N ”(311)
End (END). As a result of the comparison in (310), when N is smaller than Nmax, Nreq is set to "Nmax>Nreq".
> N ”(312) and end (EN
D).

[0021]

As described above, according to the present invention,
The database search process is divided into a server that performs the process of acquiring data from the database and a client that acquires the data from the server and processes the data. The number of acquisitions and the client memory when the client acquires the data from the server By dynamically changing the number of records held therein, there is an effect that resources can be effectively used and the waiting time of the user can be reduced without imposing an unnecessary load on the client machine.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of a database search system in a distributed environment according to the present invention.

FIG. 2 is a diagram showing an example of a processing flow of processing in a server machine according to the present invention.

FIG. 3 is a diagram showing an example of a processing flow of a memory monitoring object on a client machine according to the present invention.

FIG. 4 is a diagram showing an example of a processing flow of a data acquisition object on a client machine according to the present invention.

[Explanation of symbols]

10 user program, 20 client machine, 21 client client memory monitoring object, 22 data acquisition object, 2
3. Data access object, 24: Client machine memory, 30: Server machine, 31: Server machine memory, 32: Server machine memory monitoring object, 33: Database search object, 40
… Database.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kiyoshi Mihori 5030 Totsuka-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside Software Development Division, Hitachi, Ltd. 81-chome Hitachi Software Engineering Co., Ltd. In-house F-term (reference) 5B075 KK20 KK66 MM11 ND03 PQ05 UU40 5B082 FA02 FA03 5B089 GA11 GA21 JA12 KA05 KC44 KC48

Claims (3)

[Claims] In a data processing apparatus using a database in a distributed environment, an apparatus for pre-reading database records is prepared on a server machine, and an apparatus for dynamically determining the number of records to be acquired from the server and an available machine are provided. A record acquisition method for a database, wherein an apparatus including means for changing a timing of acquiring data according to a memory amount is provided in a client machine. 2. The database record acquisition method according to claim 1, wherein the maximum number of records read into the memory on the client machine is dynamically determined from the amount of free memory of the client machine. 3. A method of calculating the number of records to be read from a server to a client machine next time from a result of comparing past acquisition speeds when acquiring records from a server so that the acquisition speed per unit time becomes faster. Database record acquisition method characterized by the following.