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Only issue LOCK TABLE commands when necessary 

Reviewing the cases where we need to LOCK a given table during a dump,
it was pointed out by Tom that we really don't need to LOCK a table if
we are only looking to dump the ACL for it, or certain other
components.  After reviewing the queries run for all of the component
pieces, a list of components were determined to not require LOCK'ing
of the table.

This implements a check to avoid LOCK'ing those tables.

Initial complaint from Rushabh Lathia, discussed with Robert and Tom,
the patch is mine.
This commit is contained in:
Stephen Frost 2016-05-06 14:06:50 -04:00
parent 5d589993ca
commit e1b120a8cb
2 changed files with 31 additions and 1 deletions
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5
src/bin/pg_dump/pg_dump.c
View File

@ -5953,8 +5953,11 @@ getTables(Archive *fout, int *numTables)
*
* NOTE: it'd be kinda nice to lock other relations too, not only
* plain tables, but the backend doesn't presently allow that.
*
* We only need to lock the table for certain components; see pg_dump.h
*/
if (tblinfo[i].dobj.dump && tblinfo[i].relkind == RELKIND_RELATION)
if (tblinfo[i].dobj.dump && tblinfo[i].relkind == RELKIND_RELATION &&
(tblinfo[i].dobj.dump & DUMP_COMPONENTS_REQUIRING_LOCK))
{
resetPQExpBuffer(query);
appendPQExpBuffer(query,

27
src/bin/pg_dump/pg_dump.h
View File

@ -93,6 +93,33 @@ typedef uint32 DumpComponents; /* a bitmask of dump object components */
#define DUMP_COMPONENT_USERMAP (1 << 6)
#define DUMP_COMPONENT_ALL (0xFFFF)
/*
* component types which require us to obtain a lock on the table
*
* Note that some components only require looking at the information
* in the pg_catalog tables and, for those components, we do not need
* to lock the table. Be careful here though- some components use
* server-side functions which pull the latest information from
* SysCache and in those cases we *do* need to lock the table.
*
* We do not need locks for the COMMENT and SECLABEL components as
* those simply query their associated tables without using any
* server-side functions. We do not need locks for the ACL component
* as we pull that information from pg_class without using any
* server-side functions that use SysCache. The USERMAP component
* is only relevant for FOREIGN SERVERs and not tables, so no sense
* locking a table for that either (that can happen if we are going
* to dump "ALL" components for a table).
*
* We DO need locks for DEFINITION, due to various server-side
* functions that are used and POLICY due to pg_get_expr(). We set
* this up to grab the lock except in the cases we know to be safe.
*/
#define DUMP_COMPONENTS_REQUIRING_LOCK (\
DUMP_COMPONENT_DEFINITION |\
DUMP_COMPONENT_DATA |\
DUMP_COMPONENT_POLICY)
typedef struct _dumpableObject
{
DumpableObjectType objType;