INDEX PAGE WITH LATCH-FREE ACCESS

• US 20170316042A1
• Filed: 04/27/2016
• Published: 11/02/2017
• Est. Priority Date: 04/27/2016
• Status: Active Grant

• Current Assignee: SAP SE
• Original Assignee: SAP SE
• Inventors: SHE, Zheng-wei, Qian, Xu-dong, Xiong, Zhi-ping
• Granted Patent: US 10,558,636 B2
• Time in Patent Office: Days
• CPC Class Codes: G06F 16/2272 Management thereof
• CPC Class Codes: G06F 16/2282 Tablespace storage structures; Management thereof
• CPC Class Codes: G06F 16/24524 Access plan code generation and invalidation; Reuse of access plans

Abstract

Disclosed herein are system, method, and computer program product embodiments for providing read queries latch-free access to an index page. In an embodiment, a processor receives a request from a read query to access one or more records of an index page. The index page includes an update pointer and a slot array. The processor locates one or more updates prepended to the index page by locating a most recently prepended update indicated by the update pointer. Then, the processor generates a local offset table with entries in the slot array and the located one or more updates. The generated local offset table enables the processor to provide the read query access to the one or more records of the index page.

Claims

1. A computer-implemented method, comprising:

receiving a request from a read query to access one or more records of an index page that includes both an update pointer and a slot array;

locating one or more updates prepended to the index page by locating a most recently prepended update indicated by the update pointer;

generating a local offset table with entries in the slot array and the located one or more updates; and

accessing the one or more records by using the local offset table,

wherein at least one of the receiving, locating, generating, and accessing are performed by one or more computers.

2. The method of claim 1, further comprising:

performing the locating and the generating for each read query to enable the read query to access the index page concurrently with another read query or an update query.

3. The method of claim 2, wherein the update query is concurrently accessing the index page, further comprising:

consolidating the index page with the one or more prepended updates when either a number of the prepended updates exceed a threshold count or storing the one or more prepended updates requires memory exceeding a threshold amount; and

providing subsequent queries access to the consolidated index page instead of the index page.

4. The method of claim 3, further comprising:

storing, within the index page, a query count indicating a number of queries currently accessing the index page; and

responsive to generating the consolidated index page, garbage collecting the index page when the query count reaches zero.

5. The method of claim 1, further comprising:

while performing the accessing, concurrently applying an update from an update query by prepending the update to the located one or more updates; and

changing the update pointer to a pointer of the applied update.

6. The method of claim 5, further comprising:

receiving an attribute identifying an isolation level of the access request; and

determining whether to regenerate the local offset table for the read query based on the identified isolation level and information of each prepended update.

7. The method of claim 6, the determining comprising:

maintaining the generated local offset table when the isolation level precludes reading the prepended update or records requested by the read access are absent from the information.

8. The method of claim 5, further comprising:

receiving a timestamp associated with the access request;

associating the one or more prepended updates with corresponding update timestamps; and

determining whether to regenerate the local offset table for the read query by comparing the access timestamp with one or more of the update timestamps.

9. The method of claim 1, further comprising:

based on how much memory is available in the index page, storing the local offset table in the index page as a stored offset table; and

enabling a subsequent read query to locate and access records associated with the index page by using the stored offset table without requiring a subsequent local offset table to be generated for the subsequent read query.

14. The system of claim 9, the at least one processor further configured to:

while performing the access, concurrently apply an update from an update query by prepending the update to the located one or more updates; and

change the update pointer to a pointer of the applied update.

15. The system of claim 14, the at least one processor further configured to:

receive an attribute identifying an isolation level of the access request; and

determine whether to regenerate the local offset table for the read query based on the identified isolation level and information of each prepended update.

16. The system of claim 15, wherein to determine whether to regenerate the local offset table the at least one processor is configured to:

maintain the generated local offset table when the isolation level precludes reading the prepended update or records requested by the read access are absent from the information.

17. The system of claim 14, the at least one processor further configured to:

receive a timestamp associated with the access request;

associate the one or more prepended updates with corresponding update timestamps; and

determine whether to regenerate the local offset table for the read query by comparing the access timestamp with one or more of the update timestamps.

18. The system of claim 9, the at least one processor further configured to:

based on how much memory is available in the index page, store the local offset table in the index page as a stored offset table; and

enable a subsequent read query to locate and access records associated with the index page by using the stored offset table without requiring a subsequent local offset table to be generated for the subsequent read query.

10. A system, comprising:

a memory, and

at least one processor coupled to the memory and configured to;

receive a request from a read query to access one or more records of an index page that includes both an update pointer and a slot array;

locate one or more updates prepended to the index page by locating a most recently prepended update indicated by the update pointer;

generating a local offset table with entries in the slot array and the located one or more updates; and

access the one or more records by using the local offset table.

11. The system of claim 10, the at least one processor further configured to:

perform the locate and the generate for each read request to enable the read query to access the index page concurrently with another read query or an update query.

12. The system of claim 11, wherein the update query is concurrently accessing the index page, the at least one processor further configured to:

consolidate the index page with the one or more prepended updates when either a number of the prepended updates exceed a threshold count or storing the one or more prepended updates requires memory exceeding a threshold amount; and

provide subsequent queries access to the consolidated index page instead of the index page.

13. The system of claim 12, the at least one processor further configured to:

store, within the index page, a query count indicating a number of queries currently accessing the index page; and

responsive to generating the consolidated index page, garbage collect the index page when the query count reaches zero.

19. A tangible computer-readable device having instructions stored thereon that, when executed by at least one computing device, causes the at least one computing device to perform operations comprising:

receiving a request from a read query to access one or more records of an index page that includes both an update pointer and a slot array;

locating one or more updates prepended to the index page by locating a most recently prepended update indicated by the update pointer;

generating a local offset table with entries in the slot array and the located one or more updates; and

accessing the one or more records by using the local offset table.

20. The computer-readable device of claim 19, the operations further comprising:

while performing the accessing, concurrently applying an update from an update query by prepending the update to the located one or more updates;

changing the update pointer to a pointer of the applied update;

receiving an attribute identifying an isolation level of the access request; and

responsive to the changing, determining whether to regenerate the local offset table for the read query based on the identified isolation level.