Intelligent, optimistic concurrency database access scheme

• US 20020116403A1
• Filed: 12/14/2000
• Published: 08/22/2002
• Est. Priority Date: 12/14/2000
• Status: Active Grant

• Current Assignee: Borland Software Corporation (Open Text Corporation)
• Original Assignee: Borland Software Corporation (Open Text Corporation)
• Inventors: Weedon, Jonathan K.
• Granted Patent: US 6,718,349 B2
• Time in Patent Office: Days
• US Class Current: 707/201
• CPC Class Codes: G06F 16/2315 Optimistic concurrency control
• CPC Class Codes: Y10S 707/99938 Concurrency, e.g. lock management in shared database
• CPC Class Codes: Y10S 707/99952 Coherency, e.g. same view to multiple users

Abstract

Methods for minimizing conflicts in an optimistic concurrency database access scheme are described. The method provides users or software processes with cache copies of database records and tracks which data items in the cache copy were modified and whether they were read, or read before ever being modified. A decision is then made using this information as to whether the current transaction can be committed to the database. The inventive scheme engrafts intelligence to the commitment decision process and accommodates many transactions which prior art schemes consider as conflicting. Consequently, the inventive method increases throughput in such systems.

Claims

1. In an optimistic concurrency database access scheme, a method for minimizing conflicts comprising the steps of:

a) permitting multiple users to access a data record concurrently, the data record including data items having a stored value;

b) generating concurrent cache copies of the data record for each user who accesses the data record, the cache copy including an initial value for each data item amongst a set of data items within the data record, the initial value being correlated to the stored value contained in the data record;

c) permitting each user to perform a transaction on a respective cache copy by interacting with one or more data items in the cached copy, the interactions me including modifying or reading the data items;

d) for each transaction, tracking which data items were modified and whether they were read; and

e) for any transaction that includes modified data items, committing the transaction if no data item has been read, and committing the transaction if the data items that were read contain the same value as the initial value.

2. The method as in claim 1, wherein transactions are committed only if the data items that were read satisfy the further criterion that said data records were read before any modification.

3. The method as in claim 2, wherein the further criterion is satisfied in the event that there were no modifications.

4. The method as in claim 1, including the additional step of advising the user who created the transaction that the transaction failed to commit.

5. The method as in claim 1, wherein the cached copy of the set of data items includes all of the data items in the data record.

6. The method as in claim 1, wherein the tracking step comprises, for each data item, setting a first bit to indicate whether the data item was modified and a second bit to indicate whether the data item was read.

7. The method as in claim 6, wherein the logical state of the first bit is tested in determining whether the transaction includes modified data items.

8. The method as in claim 6, wherein the tracking step comprises, for each data item, setting a first bit to indicate whether the data item was modified and a second bit to indicate whether the data item was read before ever being modified.

9. The method as in claim 8, wherein the logical state of the first bit is tested in determining whether the transaction includes modified data items.

10. In an optimistic concurrency database access scheme, a method for minimizing conflicts comprising the steps of:

a) permitting multiple users to access a data record concurrently, the data record including data items having a stored value;

b) generating concurrent cache copies of the data record for each user who accesses the data record, the cache copy including an initial value for each data item amongst a set of data items within the data record, the initial value being correlated to the stored value contained in the data record;

c) permitting each user to perform a transaction on a respective cache copy by interacting with one or more data items in the cached copy, the interactions including modifying or reading the data items;

d) for each data item in the transaction, using a first bit to track whether the data item was modified and a second bit to track the occurrence of a first prescribed operation relative to a second prescribed operation on the data item; and

e) for any transaction that includes modified data items, committing the transaction in response to at least one predetermined criterion.

11. The method as in claim 10, wherein the first prescribed operation is a read operation and the second prescribed operation is a modify operation.

12. The method as in claim 11, wherein the predetermined second bit item tracks whether the read operation occurs prior to any modify operation.

13. The method as in claim 11, wherein one predetermined criterion is that the data items that were read contain the same value as the initial value.

14. The method as in claim 13, wherein another predetermined criterion is that no data item has been read.

16. The method as in claim 15, wherein transactions are committed only if the data items that were read satisfy the further criterion that said data records were read before any modification.

17. The method as in claim 15, including the additional step of advising the user who created the transaction that the transaction failed to commit.

18. The method as in claim 15, wherein the tracking step comprises, for each data item, setting a first bit to indicate whether the data item was modified and a second bit to indicate whether the data item was read.

19. The method as in claim 18, wherein the logical state of the first bit is tested in determining whether the transaction includes modified data items.

20. The method as in claim 15, wherein the tracking step comprises, for each data item, setting a first bit to indicate whether the data item was modified and a second bit to indicate whether the data item was read before ever being modified.

21. The method as in claim 20, wherein the logical state of the first bit is tested in determining whether the transaction includes modified data items.

15. In an optimistic concurrency database access scheme, a method for minimizing conflicts comprising:

a) a step for permitting multiple users to access a data record concurrently, the data record including data items having a stored value;

b) a step for generating concurrent cache copies of the data record for each user who accesses the data record, the cache copy including an initial value for each data item amongst a set of data items within the data record, the initial value being correlated to the stored value contained in the data record;

c) a step for permitting each user to perform a transaction on a respective cache copy by interacting with one or more data items in the cached copy, the interactions including modifying or reading the data items;

d) for each transaction, a step for tracking which data items were modified and whether they were read; and

e) for any transaction that includes modified data items, a step for committing the transaction if no data item has been read, and a step for committing the transaction if the data items that were read contain the same value as the initial value.