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

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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
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8
src/backend/optimizer/path/allpaths.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/path/allpaths.c,v 1.128 2005/04/25 01:30:13 tgl Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/path/allpaths.c,v 1.129 2005/04/28 21:47:13 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -214,13 +214,13 @@ set_inherited_rel_pathlist(Query *root, RelOptInfo *rel,
ListCell *il;
/*
* XXX for now, can't handle inherited expansion of FOR UPDATE; can we
* do better?
* XXX for now, can't handle inherited expansion of FOR UPDATE/SHARE;
* can we do better?
*/
if (list_member_int(root->rowMarks, parentRTindex))
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("SELECT FOR UPDATE is not supported for inheritance queries")));
errmsg("SELECT FOR UPDATE/SHARE is not supported for inheritance queries")));
/*
* Initialize to compute size estimates for whole inheritance tree