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Improve a couple of comments relating to large object snapshot management.

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This commit is contained in:
Robert Haas 2010-01-07 02:41:16 +00:00
parent 55233c3382
commit 2cb67c4c30
2 changed files with 12 additions and 15 deletions
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17
src/backend/catalog/aclchk.c
View File

@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/catalog/aclchk.c,v 1.160 2010/01/05 21:53:58 rhaas Exp $
* $PostgreSQL: pgsql/src/backend/catalog/aclchk.c,v 1.161 2010/01/07 02:41:15 rhaas Exp $
*
* NOTES
* See acl.h.
@ -3515,16 +3515,11 @@ pg_language_aclmask(Oid lang_oid, Oid roleid,
/*
* Exported routine for examining a user's privileges for a largeobject
*
* The reason why this interface has an argument of snapshot is that
* we apply a snapshot available on lo_open(), not SnapshotNow, when
* it is opened as read-only mode.
* If we could see the metadata and data from inconsistent viewpoint,
* it will give us much confusion. So, we need to provide an interface
* which takes an argument of snapshot.
*
* If the caller refers a large object with a certain snapshot except
* for SnapshotNow, its permission checks should be also applied in
* the same snapshot.
* When a large object is opened for reading, it is opened relative to the
* caller's snapshot, but when it is opened for writing, it is always relative
* to SnapshotNow, as documented in doc/src/sgml/lobj.sgml. This function
* takes a snapshot argument so that the permissions check can be made relative
* to the same snapshot that will be used to read the underlying data.
*/
AclMode
pg_largeobject_aclmask_snapshot(Oid lobj_oid, Oid roleid,

10
src/backend/catalog/pg_largeobject.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/catalog/pg_largeobject.c,v 1.36 2010/01/02 16:57:36 momjian Exp $
* $PostgreSQL: pgsql/src/backend/catalog/pg_largeobject.c,v 1.37 2010/01/07 02:41:16 rhaas Exp $
*
*-------------------------------------------------------------------------
*/
@ -251,9 +251,11 @@ LargeObjectAlterOwner(Oid loid, Oid newOwnerId)
* We don't use the system cache to for large object metadata, for fear of
* using too much local memory.
*
* Note that LargeObjectExists always scans the system catalog
* with SnapshotNow, so it is unavailable to use to check
* existence in read-only accesses.
* This function always scans the system catalog using SnapshotNow, so it
* should not be used when a large object is opened in read-only mode (because
* large objects opened in read only mode are supposed to be viewed relative
* to the caller's snapshot, whereas in read-write mode they are relative to
* SnapshotNow).
*/
bool
LargeObjectExists(Oid loid)