database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-11-06 07:49:08 +03:00
Code Activity

Implement sharable row-level locks, and use them for foreign key references

Browse Source 
to eliminate unnecessary deadlocks.  This commit adds SELECT ... FOR SHARE
paralleling SELECT ... FOR UPDATE.  The implementation uses a new SLRU
data structure (managed much like pg_subtrans) to represent multiple-
transaction-ID sets.  When more than one transaction is holding a shared
lock on a particular row, we create a MultiXactId representing that set
of transactions and store its ID in the row's XMAX.  This scheme allows
an effectively unlimited number of row locks, just as we did before,
while not costing any extra overhead except when a shared lock actually
has to be shared.   Still TODO: use the regular lock manager to control
the grant order when multiple backends are waiting for a row lock.

Alvaro Herrera and Tom Lane.
This commit is contained in:
Tom Lane
2005-04-28 21:47:18 +00:00
parent d902e7d63b
commit bedb78d386
55 changed files with 2802 additions and 439 deletions
Download Patch File Download Diff File Expand all files Collapse all files

11
src/backend/tcop/utility.c
View File

@@ -10,7 +10,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/tcop/utility.c,v 1.235 2005/04/14 01:38:18 tgl Exp $
* $PostgreSQL: pgsql/src/backend/tcop/utility.c,v 1.236 2005/04/28 21:47:15 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -238,7 +238,7 @@ QueryIsReadOnly(Query *parsetree)
if (parsetree->into != NULL)
return false; /* SELECT INTO */
else if (parsetree->rowMarks != NIL)
return false; /* SELECT FOR UPDATE */
return false; /* SELECT FOR UPDATE/SHARE */
else
return true;
case CMD_UPDATE:
@@ -1663,7 +1663,12 @@ CreateQueryTag(Query *parsetree)
if (parsetree->into != NULL)
tag = "SELECT INTO";
else if (parsetree->rowMarks != NIL)
tag = "SELECT FOR UPDATE";
{
if (parsetree->forUpdate)
tag = "SELECT FOR UPDATE";
else
tag = "SELECT FOR SHARE";
}
else
tag = "SELECT";
break;