Database garbage collector

• US 20080162610A1
• Filed: 12/30/2006
• Published: 07/03/2008
• Est. Priority Date: 12/30/2006
• Status: Active Grant

• Current Assignee: SAP SE
• Original Assignee: SAP AG (SAP SE)
• Inventors: Garstecki, Lutz, Rossmann, Albert P.
• Granted Patent: US 7,849,110 B2
• Time in Patent Office: Days
• US Class Current: 707/206
• CPC Class Codes: G06F 12/0253 Garbage collection, i.e. reclamation of unreferenced memory
• CPC Class Codes: G06F 16/24562 Pointer or reference processing operations

Abstract

A database garbage collector that removes appropriate database entries accessed during a recent transaction.

Claims

1. A method for managing a database, comprising:

beginning a first transaction;

updating a respective entry in a reference table for each object accessed during the transaction, each entry indicating any references to the object from other objects and any references from the object to other objects;

committing the first transaction;

responsive to committing the first transaction;

checking the reference table only for entries updated during the first transaction to determine for such entries whether there are any references to the corresponding object; and

deleting from the reference table any updated entry for which there is no reference to the corresponding object.

2. The method of claim 1, further comprising, responsive to committing the first transaction, deleting from the reference table any updated entry corresponding to an object referenced by a deleted updated entry.

3. The method of claim 1, further comprising, responsive to committing the first transaction, marking as “

to-delete”

from the reference table any entry corresponding to an object referenced by a deleted updated entry, when such entry corresponds to an object not accessed during the first transaction.

4. The method of claim 3, further comprising:

beginning a second transaction;

updating the entry corresponding to an object not accessed during the first transaction;

committing the second transaction;

responsive to committing the second transaction;

checking the reference table only for entries updated during the second transaction to determine for such entries whether there are any references to the corresponding object;

deleting from the reference table any updated entry for which there is no reference to the corresponding object; and

deleting the entry marked as “

to-delete” and

corresponding to the object not accessed during the first transaction.

5. An article of manufacture comprising a computer readable medium having instructions stored thereon that when executed by a machine, cause the machine to perform the following method:

beginning a first transaction;

updating a respective entry in a reference table for each object accessed during the transaction, each entry indicating any references to the object from other objects and any references from the object to other objects;

committing the first transaction;

responsive to committing the first transaction;

checking the reference table only for entries updated during the first transaction to determine for such entries whether there are any references to the corresponding object; and

deleting from the reference table any updated entry for which there is no reference to the corresponding object.

6. The article of manufacture of claim 5, the instructions, when executed, further causing the machine to perform, responsive to committing the first transaction, deleting from the reference table any updated entry corresponding to an object referenced by a deleted updated entry.

7. The article of manufacture of claim 5, further comprising instructions that when executed cause the machine to perform, responsive to committing the first transaction, marking as “

to-delete”

from the reference table any entry corresponding to an object referenced by a deleted updated entry, when such entry corresponds to an object not accessed during the first transaction.

8. The article of manufacture of claim 7, further comprising instructions that when executed by the machine cause the machine to perform the following method:

beginning a second transaction;

updating the entry corresponding to an object not accessed during the first transaction;

committing the second transaction;

responsive to committing the second transaction;

checking the reference table only for entries updated during the second transaction to determine for such entries whether there are any references to the corresponding object;

deleting from the reference table any updated entry for which there is no reference to the corresponding object; and

deleting the entry marked as “

to-delete” and

corresponding to the object not accessed during the first transaction.