JPH096656A - Data access device - Google Patents

Abstract

PURPOSE: To assure the consistency of reference data even when the data are updated and a data area is switched to another. CONSTITUTION: When the data store area of an updating object is updated (S31 to S33), this updating processing frequency is counted by a reference data pointing counter (S34). Then the data stored in a new updating object area are updated based on the data on the area to be newly referred to (S35 to S37). Furthermore, the counter value are compared with each other between the start and end modes of the processing that refers to the data store area to be referred to in response to a process request. When no coincidence is confirmed between both counter values, the reference processing is applied again to the new area.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data access device in a multi-programming computer or the like in which duplicated data is alternately updated and referred to.

[0002]

2. Description of the Related Art Conventionally, in a multi-programming computer system, etc., for data such as tables and files,
In some cases, requests for update processing and reference processing may be received from multiple processes at the same time. In that case, data is duplicated to avoid exclusive control, and update processing is performed on the one hand and reference processing is performed on the other, and alternately High-speed access and data consistency are achieved by switching the processing target. As a specific example, the access method described in Japanese Patent Laid-Open No. 3-266046 is known. This access method realizes high-speed access and guarantees data consistency by adjusting the update processing cycle by the update data aggregating device and increasing the data area switching cycle of update data and reference data. Trying to.

[0003]

However, in this conventional access method, the data update cycle is unspecified like data shared between processes of a system on a multi-programming computer (for example, a process control system). In addition, if the latestness of the reference data is required, it becomes difficult to guarantee the data consistency. In particular, if there is a process in the middle of reference processing when the data area for update data and reference data is switched, some of the data being referenced may be rewritten, and the consistency of the reference data will be lost. . The present invention has been made to solve the above problems, and the purpose thereof is to:
It is an object of the present invention to provide a data access device in which the consistency of the reference data is not always lost when the data is duplicated and accessed while switching between updating and referencing the data.

[0004]

In order to achieve the above-mentioned object, the present invention is a data processing system for executing data update and data reference processing in response to a process request while alternately switching the divided data storage areas. In the access device, a counter that counts the number of times of updating the data in the data storage area executed in response to the request of the process, and the data to be updated immediately after the update of the data storage area to be updated is requested by the process. A means for alternately switching the storage area and the data storage area of the reference target, and immediately after the switching of the data storage area, the data of the area that is the new reference target is used to store the data in the new update target area. The method of updating the data and the counter value at the start and end of the process of referencing the reference data storage area according to the process request And compare, in the case of disagreement, characterized by comprising a means for performing the reference process again.

[0005]

According to the present invention, when the data storage area to be updated is updated in response to the request of the process, the number of times of update processing is counted by the counter, and the data storage area to be updated and the data to be referred to are updated. The storage areas are switched alternately. Then, the data stored in the newly updated area is updated using the data of the newly referenced area. Further, the values of the counters at the start and end of the process of referring to the data storage area of the reference target according to the request of the process are compared, and if they do not match, the reference processing is executed again for the new area.

[0006]

Embodiments of the present invention will be described below. At first,
Explaining the outline of the embodiment, this embodiment separates the duplicated data for update and reference, uses them by switching them alternately, and performs the equivalent processing of both data separated at the time of switching. It is applied to the system. As its configuration, a reference data instruction counter that updates a value each time data is switched is prepared.

The data area switching between the update data and the reference data is basically performed in one update processing unit. However, as a property of data access, one reference processing requires a longer time than update processing and the frequency of update processing is high (such as a case where update processing is queued and continuously executed). Is the time (data area switching cycle) during which the reference data area can be referred to in the data area switching in one update processing unit.
It may be shorter than the time required for one reference processing.
Therefore, in such a case, it is necessary to shorten the time required for one reference process to be shorter than the data area switching cycle by performing the data area switching in a plurality of data update processing units.

In the basic update processing, the update data is written in the update data area and the reference data area and the update data area are switched (data area switching) by one update processing, The update data is sequentially written (data equivalent) to the data area that has been updated by the area switching. This improves the freshness of the reference data. In the reference processing, the reference data instruction counter is used to have a mechanism for determining whether or not data switching has occurred during the reference. When the switching has occurred, the reference processing is performed again to update the data. It is possible to avoid referring to data during processing (during data equalization).

Next, an embodiment will be specifically described with reference to the drawings. FIG. 1 is an explanatory diagram showing a data structure in the first embodiment. In this embodiment, a reference data instruction counter is prepared to identify the update data and the reference data. The reference data instruction counter has an initial value of 0 and is incremented by 1 each time data switching occurs, so that the value differs before and after data switching. The reference data is identified by setting the value of this reference data instruction counter to 2
It is performed by discriminating the remainder (0, 1) when divided by. That is, by using this value (0, 1) as the array element number of the pointer array to the area, it becomes possible to easily obtain the address to the data area. Data equalization is performed on the two data areas at the time of initialization.

FIG. 2 is a diagram showing the relationship between the data access processing and the two areas in the first embodiment. When the data area A is linked to the 0th pointer array to the area, the data area A becomes the reference area immediately after initialization.
When the data updating process occurs, the data is updated in the data area B. When the data update to the data area B is completed, the areas for reference data and update data are switched. As a result, the data area A becomes the update data area and the data area B becomes the reference data area. At this point, since the updated data by the previous update processing is not reflected in the data area A, data equalization with the data area B is performed. By repeating the above, data access is performed.

FIG. 3 is a flow chart showing the update processing procedure of the first embodiment. In the update process, first, the remainder obtained by dividing the reference data instruction counter by 2 is obtained, and the value (Y) is checked (S31). If the value is 0, the address of the first linked data area (data area B in FIG. 1) of the pointer array to the area is acquired, and the data is updated to that area (S32). When the value is 1, the address of the 0th linked data area (data area A) of the pointer array to the area is acquired, and the data is updated for that area (S33). After the data update is completed, the value of the reference data instruction counter is incremented (S34), and the reference data area is switched.
That is, when Y = 0 in S31, the reference data area is switched from the data area A to the data area B.

Next, Y is checked (S35). If Y is 1, the data updated in S32 is not reflected in the area (data area A) that has become the update data area due to the data area switching at this point. Therefore, the data updated in S32 is also updated (data equivalent) in this area (data area A), so that both data area A and data area B are made the latest data (S36). Y
Is 0, the area (data area B) that has become the update data area due to the data area switching at this point is S33.
The data updated in is not reflected. Therefore, S33
By updating the data updated in (1) to this area (data area B) (data equivalent), the data area A
And the data area B are both set to the latest data (S37).
It should be noted that a plurality of update processes are not performed at the same time, and the update processes that have occurred are performed sequentially.

FIG. 4 is a flow chart showing the reference processing procedure. In the reference process, first, the value of the reference data instruction counter is stored (S41). Next, as in the update process, the remainder obtained by dividing the reference data instruction counter by 2 is obtained,
The value is checked (S42). If the value is 0, the address of the 0th linked data area (data area A) of the pointer array to the area is acquired and the data is referred to from that area (S43). If the value is 1,
The address of the first linked data area (data area B) in the pointer array to the area is acquired and referenced from that area (S45). After the end of the data reference, the current value (X) of the reference data instruction counter and the variable N in S41.
The values stored in are compared (S44). If X and N do not match, it means that the data area switching has occurred during the data reference, so the data equalization processing (S34
~ S37), there is a possibility that a part of the referred data has been updated. Therefore, by repeating the reference process again from the beginning, consistent data reference is possible.

In the above-mentioned method, the data area is switched every one update process, so that the reference process can obtain the latest data. However, if the data access has a property that one reference process requires a longer time than one update process and the update process occurs frequently, the data area switching cycle is one time. It may be shorter than the reference process. In such a case, as shown in FIG. 5, data area switching is performed a plurality of times (two times in the example).
This can be dealt with by making the time required for one reference processing shorter than the cycle of data area switching by performing the update processing every time. The second embodiment implements this processing. The second embodiment can be easily realized by changing the update process of the first embodiment.

FIG. 6 is a flow chart showing the processing of the second embodiment, in which the data area is switched every time the data is updated a plurality of times. Regarding S61 to S63, S31 to S3
Similar to 3, the data is updated in the update data area. After updating the data, the update counter (I) is incremented (S64). It is checked whether or not the updated update counter has reached a predetermined update count (J) (S65). If it has arrived, the data area is switched as in S34 (S66). Then, S67
In steps S69 to S69, data equalization processing is performed as in steps S35 to S37. However, the data equivalent in this case is the data area A,
It is done by copying between B. After the data equivalence is completed, the update counter (I) is reset (S70).

According to the above-described embodiment, it is possible to recognize that data switching has occurred in the reference process. Therefore, if the data area is switched without synchronizing the update processing and the reference processing, even if a part of the in-reference data is rewritten by the data equivalence processing when the data area is switched, By re-executing the process, it is possible to avoid referring to the data being updated as it is. That is, if the reference process requires a longer time than the update process and the data access does not have a special property such as a high occurrence frequency of the update process, it is possible to refer to the data immediately after the update,
The up-to-dateness of reference data is improved.

[0017]

As described above, according to the present invention, the data storage area is alternately switched after the data is updated by the process, and the data of the area newly referred to is used as the new update target. When the update processing of the data stored in the area is performed, if the reference processing by another process is being performed, the reference processing for the new area is re-executed. As a result, the consistency of the reference data is always guaranteed.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a data structure according to a first embodiment of this invention.

FIG. 2 is a timing chart illustrating the operation of the first embodiment.

FIG. 3 is a flowchart illustrating update and switching processing according to the first embodiment.

FIG. 4 is a flowchart illustrating a reference process according to the first embodiment.

FIG. 5 is a timing chart explaining the operation of the second embodiment.

FIG. 6 is a flowchart illustrating processing of the second embodiment.

Claims (1)

[Claims] 1. A data access device for executing a data update process and a data reference process in response to a request from a process while alternately switching the divided data storage region, the data storage region being executed in response to the process request. A counter for counting the number of times the data is updated, and a means for switching between the update target data storage area and the reference target data storage area immediately after the update target data storage area is updated by a process request. Immediately after switching the data storage area, a means for updating the data stored in the newly updated area using the data in the newly referenced area, and the reference object in response to the process request If the values of the counters at the start and end of the process that refers to the data storage area of are compared, and they do not match, the reference process is executed again. Data access apparatus, comprising the, the.