Changing concurrency control modes

Patent metadata

Field	Value
Publication number	US-2018322158-A1
Application number	US-201715585153-A
Country	US
Kind code	A1
Filing date	May 2, 2017
Priority date	May 2, 2017
Publication date	Nov 8, 2018
Grant date	—

Abstract

Example implementations relate to changing concurrency control modes. An example implementation includes controlling a concurrency control mode of a data slot that stores a data value. A concurrency control mode of a data slot may be changed from an optimistic concurrency control mode to a multi-version concurrency control mode responsive to detecting a read-write conflict for the data slot. A concurrency control mode of a data slot may be changed from a multi-version concurrency control mode to an optimistic concurrency control mode responsive to detecting that the data slot satisfies a low contention criterion.

First claim

What is claimed is:

1 . A method comprising:
controlling a concurrency control mode of a data slot that stores a data value, wherein the concurrency control mode determines how a transaction is handled responsive to a read-write conflict, and controlling the concurrency control mode comprises:
responsive to detecting a read-write conflict for the data slot, changing the concurrency control mode from an optimistic concurrency control mode to a multi-version concurrency control mode; and
changing the concurrency control mode from the multi-version concurrency control mode to the optimistic concurrency control mode responsive to detecting that the data slot satisfies a low contention criterion.

2 . The method of claim 1 , where the read-write conflict for the data slot is detected by:
comparing a first version of the data value read at a first time with a second version of the data value read at a second time different than the first time; and determining that the first version and the second version are different.

3 . The method of claim 2 , wherein the data value read at the first time is read during an execution phase of the transaction and the data value read at the second time is read during a validation phase of the transaction.

4 . The method of claim 1 , wherein the read-write conflict for the data slot is detected by:
assigning a transaction timestamp to the transaction; and determining that the transaction timestamp is earlier in time than a commit time of the stored data value.

5 . The method of claim 4 , wherein, when in the optimistic concurrency control mode, the transaction is aborted responsive to detecting that the transaction timestamp is earlier in time than a commit time of the stored data value.

6 . The method of claim 1 , wherein an additional version of the stored data value is stored within a transaction record and is assigned a commit time.

7 . The method of claim 6 , wherein any additional version of the stored data value stored within a transaction record is located by a version chain locator in the data slot.

8 . The method of claim 7 , wherein the transaction record is in a per-thread ring buffer and the additional version of the stored data value is ordered by commit time in a version chain located by the version chain locator.

9 . The method of claim 8 , wherein the low contention criterion is satisfied where the version chain locator in the data slot does not locate any created additional version of the stored data value.

10 . The method of claim 1 , wherein, when in the optimistic concurrency control mode, a write of the transaction is updated to an optimistic concurrency buffer in a transaction record of the transaction, and wherein the transaction record comprises the optimistic concurrency control buffer and a multi-version concurrency control buffer.

11 . The method of claim 10 , wherein the transaction record further comprises a transaction status field to indicate a transaction status of the transaction.

12 . The method of claim 10 , wherein the optimistic concurrency control buffer is stored within a per-thread ring buffer, and wherein the optimistic concurrency control buffer is reclaimed upon a commit of the transaction.

13 . The method of claim 1 , wherein, when in the multi-version concurrency control mode, a write of the transaction is updated to a multi-version concurrency control buffer in a transaction record of the transaction.

14 . A system comprising:
a processor; and a set of memory resources storing:
a data slot comprising:
a committed in-place data value; and
a mode indicator to indicate whether a concurrency control mode of the data slot is in an optimistic concurrency control mode that aborts a transaction upon detecting a read-write conflict, or a multi-version concurrency control mode that creates an additional version of the committed data value responsive to detecting the read-write conflict; and

instructions in memory to be executed by a processor, the instructions when executed to:
change the concurrency control mode from the optimistic concurrency control mode to the multi-version concurrency control mode responsive to detecting the read-write conflict for the data slot; and
change the concurrency control mode from the multi-version concurrency control mode to the optimistic concurrency control mode responsive to detecting that the data slot satisfies a low contention criterion.

15 . The system of claim 14 , wherein the data slot further comprises a version chain locator to locate any created additional version of the committed data value.

16 . The system of claim 15 , wherein the data slot further comprises a priority indicator to indicate whether a read should first occur from the committed in-place data value of the data slot or the version chain locator of the data slot.

17 . The system of claim 15 , wherein the low contention criterion is satisfied where the version chain locator of the data slot does not locate any created additional version of the committed data value.

18 . The system of claim 15 , wherein the instructions in memory further comprise instructions to assign a commit timestamp to an additional version of the committed data value upon validation of the additional version, and wherein the validated additional version is ordered by commit time.

19 . A non-transitory computer-readable medium comprising instructions executable by a processor to:
detect a read-write conflict for a data slot; responsive to detecting the read-write conflict, change a concurrency control mode of the data slot from an optimistic concurrency control mode that aborts a transaction upon detecting a read-write conflict, to a multi-version concurrency control mode that creates an additional version of the stored data value; detect that a version chain locator of the data slot does not point to any additional version of the stored data value; responsive to detecting that the version chain locator does not point to any additional version of the stored data value, change the concurrency control mode from the multi-version concurrency control mode to the optimistic concurrency control mode.

20 . The non-transitory computer-readable medium of claim 19 , wherein the read-write conflict is detected by:
assigning a transaction timestamp to a received transaction; and determining that the transaction timestamp is earlier in time than a commit time of a stored data value in the data slot.

Assignees

• Hewlett Packard Entpr Dev Lp

Inventors

• Zhang Huanchen
• Keeton Kimberly

Classifications

• G06F17/30353

  Physics · mapped topic

• G06F17/30362 Primary

  Physics · mapped topic

• G06F17/30356

  Physics · mapped topic

• G06F16/2322 Primary

  using timestamps · CPC title

• G06F16/2343 Primary

  Locking methods, e.g. distributed locking or locking implementation details · CPC title