JPH04355843A - Storage device - Google Patents

Abstract

PURPOSE:To shorten the time required for the change of the storage state and to reduce the amount of required hardware by allowing the write history to remain in a write history holding means at the time of writing data in a storage means indicated by a latest state display means. CONSTITUTION:Data is written in one of plural storage means 20 by a data write means 10. A write history holding means 30 holds the write or the non- write to storage means 20, and one of plural storage means which holds the latest state is indicated by a latest state display means 40. The data write means 10 refers to the latest state display means 40 to write data in the storage means 20 indicated by this means 40. At the time of this write, the write history is allowed to remain in the write history holding means 30. Thus, it is sufficient if a pointer is switched to the data holding position without transferring the actual body of data at the time of return to the state at a certain time, and therefore, redundant data transfer is avoided.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a storage device that maintains a memory state at a certain point in time and allows the memory state to be restored.

0002

2. Description of the Related Art In a conventional storage device for retaining a memory state at a certain point in time and restoring the memory state, a plurality of storage means are arranged to maintain the memory state at each point in time to cope with this problem. (For example, W. Hwu and Y. Patt:
”Checkpoint Repair for H
right-Performance Out-of-Or
der Execution Machines”,
IEEE Transactions on Comp
uters, Vol. C-36, No. 12, pp. 1
496-1514, Dec. 1987). In this storage device, the entire storage state is transferred between a plurality of storage means as shown in FIG. 4, thereby making it possible to restore the storage state.

0003

However, in the above-mentioned storage device, as the amount of storage per storage state increases, the time cost and hardware cost required for transfer increase, resulting in a problem in terms of efficiency. As described above, conventional storage devices have problems that need to be solved regarding transfer time and hardware costs. An object of the present invention is to provide a highly efficient storage device by eliminating such conventional problems and avoiding redundant data transfer.

0004

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides a storage device that enables restoration of a storage state by retaining a storage state at a certain point in time.
A first means for writing data, a plurality of second means for writing the data by the first means and storing the data, and a history of data writing by the first means to the second means. and a fourth means for displaying which one of the plurality of second means contains the latest state.
means, and the second means is managed for each of a plurality of words.

[0005]

[Operation] By taking such a means, when returning to a state at a certain point in time, it is possible to simply switch the pointer to the location where the data is held, without transferring the actual data. This avoids redundant data transfer and provides an efficient storage device.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, numeral 10 denotes data writing means for writing data into the storage means. 20 is a storage means, and data is written into any one of the plurality of storage means 20 from the data writing means 10. Reference numeral 30 denotes a write history holding means for holding whether or not writing has been performed on the storage means 20. Reference numeral 40 denotes a latest state display means for indicating which of the plurality of storage means holds the latest state.

FIG. 2 shows the format of the write history holding means 30. This format corresponds to the number n of words in the storage means 20 and the number m of the storage means 20. Writing history holding means 30
If we write the i-th word of the j-th storage state as BH[j,i], "BH[j,i]=1" means that there is a write to the i-th word of the j-th storage means. It is shown that.

FIG. 3 shows the format of the latest status display means 40. This format corresponds to the number of words n in the storage means 20. If the i-th word of the latest state display means 40 is written as WC[i], "WC[i]=j" means that the latest storage state of the i-th word is in the j-th storage means. It shows.

The contents of the present invention will be explained in connection with a storage device having the above configuration. First, the operation when writing data will be explained. Data written from the data writing means 10 is stored in one of the storage means 20. The latest status display means 40 determines which storage means 20 to write to.
Follow. That is, when attempting to write to the i-th word, the i-th word WC[i] of the latest status display means 40
(=j) and writes to the j-th storage means. During this writing, BH[j,i] is set to 1 in the i-th word of the j-th storage state of the writing history holding means 30, and the writing history is left.

Next, the operation when saving the memory state (checkpoint) will be explained. A maximum of m checkpoints (the number of possible storage states of the write history holding means 30) can be saved at the same time. Let HP be the latest storage state number in the write history holding means 30, and TP be the oldest storage state number. Both HP and TP take values from 1 to m, and the initial state is 1. HP is always incremented ahead of TP. When performing a checkpoint, BH, which is the i-th word of the j-th storage state of the writing history holding means 30, is
Add [j,i] (mod m). However, i is 1~
for all n, and j is HP. Next, HP is incremented (mod m) and BH[HP,i] of the write history holding means 30 is set to 0. However, when performing this checkpoint, (HP+1) must be ≠ TP.

Next, the operation when restoring to the previous storage state will be explained. When performing restoration, from WC[i] which is the i-th word of the latest state display means 40 to BH[j, which is the i-th word of the j-th storage state of the writing history holding means 30
i] (mod m). However, i is all of 1 to n, and j is TP. Next, HP is decremented (mod m). To discard the oldest storage state, increment TP (mod m
)do.

The operation of the present invention described above will be summarized below. However, WC[i] is the latest storage means number (=1 to m) of the i-th word, and BH[j,i] is the "i-th storage means number of the j-th storage state".
History of writing to “word” (=1 indicates writing exists), H
P represents the latest storage state number in BH, TP represents the oldest storage state number in BH, and WN represents the word number to be written. Initial state WC[i]←0 (i=1
~n) BH[1,i]←0 (i=
1 to n) HP←1 TP←1 When writing BH [WC[WN], WN]←1 When creating the latest backup state i
f(HP+1)≠TP then
WC[i]←WC[i]+BH[HP,i] (m
od m)

(i=1~n)
HP←HP+1 (mod m)
BH[HP,i]←0
(i=1
~n) When restoring to the previous backup state WC[i]←WC[i]-BH[HP,i
] (mod m)

(i=1~n
) HP←HP-1 (mod m) When discarding the oldest backup state TP←TP+1 (mod m)

[0013]

[Effects of the Invention] As is clear from the above explanation, according to the present invention, compared to the conventional storage device which transfers the entire storage means, by performing fine control on a word-by-word basis,
It is possible to provide an efficient storage device with little waste and low time cost and hardware cost for changing the storage state.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing the configuration of write history holding means in FIG. 1;

FIG. 3 is a diagram showing the configuration of latest status display means in FIG. 1;

FIG. 4 is a configuration diagram according to a conventional technique.

[Explanation of symbols]

10 Data writing means 20 Memory means 30 Writing history retention means 40 Latest status display means

Claims (1)

[Claims] Claims: 1. A storage device capable of restoring a storage state by retaining the storage state at a certain point in time, comprising: first means for writing data; A plurality of second means for storing data, a third means for retaining a history of data writing to the second means by the first means, and one containing the latest state among the plurality of second means. and fourth means for displaying which one is, and the second means is managed for each of a plurality of words.