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Give SMgrRelation pointers a well-defined lifetime.

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After calling smgropen(), it was not clear how long you could continue
to use the result, because various code paths including cache
invalidation could call smgrclose(), which freed the memory.

Guarantee that the object won't be destroyed until the end of the
current transaction, or in recovery, the commit/abort record that
destroys the underlying storage.

smgrclose() is now just an alias for smgrrelease(). It closes files
and forgets all state except the rlocator, but keeps the SMgrRelation
object valid.

A new smgrdestroy() function is used by rare places that know there
should be no other references to the SMgrRelation.

The short version:

 * smgrclose() is now just an alias for smgrrelease(). It releases
   resources, but doesn't destroy until EOX
 * smgrdestroy() now frees memory, and should rarely be used.

Existing code should be unaffected, but it is now possible for code that
has an SMgrRelation object to use it repeatedly during a transaction as
long as the storage hasn't been physically dropped.  Such code would
normally hold a lock on the relation.

This also replaces the "ownership" mechanism of SMgrRelations with a
pin counter.  An SMgrRelation can now be "pinned", which prevents it
from being destroyed at end of transaction.  There can be multiple pins
on the same SMgrRelation.  In practice, the pin mechanism is only used
by the relcache, so there cannot be more than one pin on the same
SMgrRelation.  Except with swap_relation_files XXX

Author: Thomas Munro, Heikki Linnakangas
Reviewed-by: Robert Haas <robertmhaas@gmail.com>
Discussion: https://www.postgresql.org/message-id/CA%2BhUKGJ8NTvqLHz6dqbQnt2c8XCki4r2QvXjBQcXpVwxTY_pvA@mail.gmail.com
This commit is contained in:
Heikki Linnakangas
2024-01-31 12:31:02 +02:00
parent 6a8ffe812d
commit 21d9c3ee4e
12 changed files with 188 additions and 232 deletions
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2
src/backend/utils/cache/inval.c vendored
View File

@@ -756,7 +756,7 @@ LocalExecuteInvalidationMessage(SharedInvalidationMessage *msg)
rlocator.locator = msg->sm.rlocator;
rlocator.backend = (msg->sm.backend_hi << 16) | (int) msg->sm.backend_lo;
smgrcloserellocator(rlocator);
smgrreleaserellocator(rlocator);
}
else if (msg->id == SHAREDINVALRELMAP_ID)
{

21
src/backend/utils/cache/relcache.c vendored
View File

@@ -3044,7 +3044,7 @@ RelationCacheInvalidate(bool debug_discard)
* start to rebuild entries, since that may involve catalog fetches which
* will re-open catalog files.
*/
smgrcloseall();
smgrdestroyall();
/* Phase 2: rebuild the items found to need rebuild in phase 1 */
foreach(l, rebuildFirstList)
@@ -3066,25 +3066,6 @@ RelationCacheInvalidate(bool debug_discard)
in_progress_list[i].invalidated = true;
}
/*
* RelationCloseSmgrByOid - close a relcache entry's smgr link
*
* Needed in some cases where we are changing a relation's physical mapping.
* The link will be automatically reopened on next use.
*/
void
RelationCloseSmgrByOid(Oid relationId)
{
Relation relation;
RelationIdCacheLookup(relationId, relation);
if (!PointerIsValid(relation))
return; /* not in cache, nothing to do */
RelationCloseSmgr(relation);
}
static void
RememberToFreeTupleDescAtEOX(TupleDesc td)
{