JPS63317823A - Data access system by index - Google Patents

Abstract

PURPOSE:To reduce the area size of an index in case of many data records and a small number of types of value secured for an index key, by obtaining the address of the data corresponding to a supplied index key via a bit map access mechanism. CONSTITUTION:A data processing system has a request for return of the address of the data record having the value (b) of an index field 20 out of those data records stored in a data file 10. Thus the control is shifted to a data access mechanism 1 and an index access mechanism 2. Then an access is supplied to an index 30 so that the address of a bit map 70 having the address information on the data record having the value (b) of the field 20 is obtained. Then the control is shifted to a bit map access mechanism 3 and an access is given to the map 70. Thus the address of the data record having the value (b) of the field 20 is obtained and sent back to the data processing system.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for accessing data using an index, and in particular, a method for accessing data using an index for files and databases containing a large number of data items. By accessing the index 80 consisting of four interfaces 100 using the index access mechanism 7, the data access mechanism 6 obtains the address of data having a given index key 90. was.

If there are multiple pieces of data with the same index key,
The method was to have as many pointers 100 to the data.

[Problem that the invention seeks to solve]

In the conventional index-based data access method described above,
When there are multiple pieces of data with the same index key, the method is to have pointers to that number of data, so if the number of data items is large and the types of values taken by the index are extremely small, As the number of data with index keys increases, the area of the index that is accessed to find the address of data with a given index key also increases, and the time required to find the address of data with a given index key increases. There is a problem that it takes.

The present invention solves the above-mentioned problems of the conventional methods and provides an index-based data access method that allows the address of data having a given index key to be found in a short time.

[Means for solving problems]

The data access method using an index according to the present invention includes an index access mechanism that obtains the address of a pit map corresponding to the index key by accessing the index when an index key is given, and accesses the pit map corresponding to the index key. The data access mechanism includes a pit map access mechanism that obtains the address of data, and a data access mechanism that accesses data from the address of the data.

〔Example〕

Next, two aspects of the present invention will be explained with reference to the drawings.

FIG. 1 is a schematic diagram of the configuration of an embodiment of the present invention, and FIG. 2 is a diagram showing the flow of its operation.

Assume that a request is issued from the data processing system to return the address of a data record whose index field 20 has a value of b among the data records of the data file 10.

Control is by data access mechanism 1. By accessing the index 30 with the index access mechanism 2, the address of the bitmap 70 having the address information of the data record whose index field 20 has the value b is determined.

Next, control is transferred to the pit map access mechanism 3, and by accessing the bit map f70f, the address of the data record whose index field l-"20 has the value b is determined and returned.

Here, in FIGS. 2 and 4, the number of data records in the constant data file 10 is calculated using the index key 40.
The byte length of 90 is the byte index key 40. The number of values that 90 takes is m types Pointer to the pit map Byte length of 50 t - p bytes Pointer to the data record The byte length of 100 is q bytes The book in Figure 1 The size of the index area (including the bitmap area) in one embodiment of the invention is as follows.

The area size of the index in the case of the conventional method shown in FIG.

(k+q)·n strong bytes - Equation (2) is acceptable; it becomes larger as the number of index layers increases.

When the number of data records n is large and the number m of types of values taken by the index key is extremely small.

8. (k + q) (2) formula / (1) formula □ ... (3) Second, the area size of the index in the case of the conventional method is.

This is 8° (k+q) times that in the case of the present invention.

Here's a temporary one.

Assuming that the byte length of the index key is kil bytes and the byte length of the pointer to the data record is qt - 4 bytes, and the number of types of values that the index key can take is mt2.4.8, then from equation (3), in the case of the conventional method, The area size of the index is 20°10.5 times that in the case of the present invention.

From the above, if the number of data records is large and the value type expression taken by the index key is extremely small.

It can be seen that the area size of the index is smaller in the case of the present invention.

Even when finding the address of data with a given index key, the area size of the index to be accessed is smaller in the case of the present invention, and the address of data having the given index key can be found quickly. can.

In addition, in the case of the conventional method, the index has a hierarchical structure, and the index is divided into blocks.

However, in the case of the present invention, since the index can be small, such a problem is less likely to occur.

[Effects of the Invention] As explained above, in the present invention, the address of a bitmap corresponding to a given index key is found by an index access mechanism, and the address of data corresponding to the given index key is found by a bitmap access mechanism. Therefore, when the number of data items is large and the types of values taken by the index are extremely small, the index area (including the bitmap area) can be reduced compared to the conventional method.

The index area (including the bitmap area) that is accessed to find the address of data with a given index key is smaller than in the conventional method, and there is very little problem of increased input/output due to index division. This has the effect of quickly finding the address of data with a given index key.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of the configuration of an embodiment of the present invention, Fig. 2 is a diagram showing the flow of its operation, Fig. 3 is a schematic diagram of the configuration of an example of the conventional method, and Fig. 4 is the flow of its operation. 0 1.6...Data access mechanism, 2,7... Index access mechanism, 3... Bitmap access mechanism. 10...Data file, 20...Index field. 30.80...index, 40...index key, 50...
- Pointer to bitmap, 60.70...Bitmap f, 90...-* pull key, 100... Pointer to data record. Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. In a data processing device having a file device such as a magnetic disk device, index access for obtaining the address of a bitmap corresponding to the index key by accessing the index when an index key is given. a bitmap access mechanism that obtains an address of data by accessing a bitmap corresponding to the index key; and a data access mechanism that accesses data from the address of the data. Data access method.