On Wed, Jul 06, 2011 at 08:35:55PM -0400, Robert Haas wrote:
> On Wed, Jul 6, 2011 at 6:32 PM, Noah Misch <n...@2ndquadrant.com> wrote:
> > While a mere "LOCK bar.x" is sufficient to get a clean cutover with respect
> > to
> > parsing, it fails to invalidate plans. To really cover all bases, you need
> > some no-op action that invalidates "bar.x". For actual practical use, I'd
> > recommend something like:
> >
> > BEGIN;
> > ALTER TABLE bar.x RENAME TO x0;
> > ALTER TABLE bar.x0 RENAME TO x;
> > CREATE TABLE foo.x ...
> > COMMIT;
> >
> > Probably worth making it more intuitive to DTRT here.
>
> Well, what would be really nice is if it just worked.
Yes.
> Care to submit an updated patch?
Attached. I made the counter 64 bits wide, handled the nothing-found case per
your idea, and improved a few comments cosmetically. I have not attempted to
improve the search_path interposition case. We can recommend the workaround
above, and doing better looks like an excursion much larger than the one
represented by this patch.
Thanks,
nm
diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index c9b1d5f..a345e39 100644
*** a/src/backend/access/heap/heapam.c
--- b/src/backend/access/heap/heapam.c
***************
*** 975,1000 **** relation_openrv(const RangeVar *relation, LOCKMODE lockmode)
{
Oid relOid;
! /*
! * Check for shared-cache-inval messages before trying to open the
! * relation. This is needed to cover the case where the name
identifies a
! * rel that has been dropped and recreated since the start of our
! * transaction: if we don't flush the old syscache entry then we'll
latch
! * onto that entry and suffer an error when we do RelationIdGetRelation.
! * Note that relation_open does not need to do this, since a relation's
! * OID never changes.
! *
! * We skip this if asked for NoLock, on the assumption that the caller
has
! * already ensured some appropriate lock is held.
! */
! if (lockmode != NoLock)
! AcceptInvalidationMessages();
!
! /* Look up the appropriate relation using namespace search */
! relOid = RangeVarGetRelid(relation, false);
/* Let relation_open do the rest */
! return relation_open(relOid, lockmode);
}
/* ----------------
--- 975,985 ----
{
Oid relOid;
! /* Look up and lock the appropriate relation using namespace search */
! relOid = RangeVarLockRelid(relation, lockmode, false);
/* Let relation_open do the rest */
! return relation_open(relOid, NoLock);
}
/* ----------------
***************
*** 1012,1041 **** relation_openrv_extended(const RangeVar *relation, LOCKMODE
lockmode,
{
Oid relOid;
! /*
! * Check for shared-cache-inval messages before trying to open the
! * relation. This is needed to cover the case where the name
identifies a
! * rel that has been dropped and recreated since the start of our
! * transaction: if we don't flush the old syscache entry then we'll
latch
! * onto that entry and suffer an error when we do RelationIdGetRelation.
! * Note that relation_open does not need to do this, since a relation's
! * OID never changes.
! *
! * We skip this if asked for NoLock, on the assumption that the caller
has
! * already ensured some appropriate lock is held.
! */
! if (lockmode != NoLock)
! AcceptInvalidationMessages();
!
! /* Look up the appropriate relation using namespace search */
! relOid = RangeVarGetRelid(relation, missing_ok);
/* Return NULL on not-found */
if (!OidIsValid(relOid))
return NULL;
/* Let relation_open do the rest */
! return relation_open(relOid, lockmode);
}
/* ----------------
--- 997,1011 ----
{
Oid relOid;
! /* Look up and lock the appropriate relation using namespace search */
! relOid = RangeVarLockRelid(relation, lockmode, missing_ok);
/* Return NULL on not-found */
if (!OidIsValid(relOid))
return NULL;
/* Let relation_open do the rest */
! return relation_open(relOid, NoLock);
}
/* ----------------
diff --git a/src/backend/catalog/namespindex ce795a6..f75fcef 100644
*** a/src/backend/catalog/namespace.c
--- b/src/backend/catalog/namespace.c
***************
*** 44,49 ****
--- 44,51 ----
#include "parser/parse_func.h"
#include "storage/backendid.h"
#include "storage/ipc.h"
+ #include "storage/lmgr.h"
+ #include "storage/sinval.h"
#include "utils/acl.h"
#include "utils/builtins.h"
#include "utils/guc.h"
***************
*** 285,290 **** RangeVarGetRelid(const RangeVar *relation, bool failOK)
--- 287,372 ----
}
/*
+ * RangeVarLockRelid
+ * Like RangeVarGetRelid, but simultaneously acquire the specified
lock
+ * on the relation. This works properly in the face of concurrent
DDL
+ * that may drop, create or rename relations.
+ *
+ * If the relation is not found and failOK = true, take no lock and return
+ * InvalidOid. Otherwise, raise an error.
+ */
+ Oid
+ RangeVarLockRelid(const RangeVar *relation, LOCKMODE lockmode,
+ bool failOK)
+ {
+ int lastCounter;
+ Oid relOid1,
+ relOid2;
+
+ /*
+ * If the caller requested NoLock, it already acquired an appropriate
lock
+ * with LockRelationOid(). In this case, our first search is always
+ * correct, and we degenerate to RangeVarGetRelid().
+ */
+ if (lockmode == NoLock)
+ return RangeVarGetRelid(relation, failOK);
+
+ /*
+ * By the time we acquire the lock, our RangeVar may denote a different
+ * relation or no relation at all. In particular, this can happen when
+ * the lock acquisition blocks on a transaction performing DROP or ALTER
+ * TABLE RENAME. However, once and while we do hold a lock of any
level,
+ * we can count on the name of the found relation remaining stable.
+ *
+ * Even so, DDL activity could cause an object in a schema earlier in
the
+ * search path to mask our original selection undetected. No current
lock
+ * would prevent that. We let the user worry about it, such as by
taking
+ * additional explicit locks.
+ */
+
+ /*
+ * First attempt. Always allow it to fail; RangeVarGetRelid() may hit a
+ * negative catcache entry for a recently-created relation. Find out by
+ * making recent DDL effects visible and checking again. Attempting to
+ * open nonexistent relations is not a hot path in applications, so the
+ * extra cost is of little concern.
+ */
+ lastCounter = SharedInvalidMessageCounter;
+ relOid1 = RangeVarGetRelid(relation, true);
+ if (!OidIsValid(relOid1))
+ {
+ AcceptInvalidationMessages();
+ lastCounter = SharedInvalidMessageCounter;
+ relOid1 = RangeVarGetRelid(relation, failOK);
+ }
+
+ do
+ {
+ /* After the initial precautions above, not-found is final. */
+ if (!OidIsValid(relOid1))
+ return relOid1;
+
+ /*
+ * LockRelationOid() also calls AcceptInvalidationMessages() to
make
+ * recent DDL effects visible, if needed. Finding none, we're
done.
+ */
+ LockRelationOid(relOid1, lockmode);
+ if (lastCounter == SharedInvalidMessageCounter)
+ break;
+ else
+ lastCounter = SharedInvalidMessageCounter;
+
+ /* Some invalidation messages arrived; search again. */
+ relOid2 = relOid1;
+ relOid1 = RangeVarGetRelid(relation, failOK);
+
+ /* Done when our RangeVar denotes the same relation we locked.
*/
+ } while (relOid1 != relOid2);
+
+ return relOid1;
+ }
+
+ /*
* RangeVarGetCreationNamespace
* Given a RangeVar describing a to-be-created relation,
* choose which namespace to create it in.
diff --git a/src/backend/storage/ipc/sindex 9ab16b1..8499615 100644
*** a/src/backend/storage/ipc/sinval.c
--- b/src/backend/storage/ipc/sinval.c
***************
*** 22,27 ****
--- 22,30 ----
#include "utils/inval.h"
+ uint64 SharedInvalidMessageCounter;
+
+
/*
* Because backends sitting idle will not be reading sinval events, we
* need a way to give an idle backend a swift kick in the rear and make
***************
*** 90,95 **** ReceiveSharedInvalidMessages(
--- 93,99 ----
{
SharedInvalidationMessage *msg = &messages[nextmsg++];
+ SharedInvalidMessageCounter++;
invalFunction(msg);
}
***************
*** 106,111 **** ReceiveSharedInvalidMessages(
--- 110,116 ----
{
/* got a reset message */
elog(DEBUG4, "cache state reset");
+ SharedInvalidMessageCounter++;
resetFunction();
break; /* nothing more to do */
}
***************
*** 118,123 **** ReceiveSharedInvalidMessages(
--- 123,129 ----
{
SharedInvalidationMessage *msg = &messages[nextmsg++];
+ SharedInvalidMessageCounter++;
invalFunction(msg);
}
diff --git a/src/backend/storage/lmgr/lindex 859b385..90b2ecc 100644
*** a/src/backend/storage/lmgr/lmgr.c
--- b/src/backend/storage/lmgr/lmgr.c
***************
*** 81,90 **** LockRelationOid(Oid relid, LOCKMODE lockmode)
/*
* Now that we have the lock, check for invalidation messages, so that
we
* will update or flush any stale relcache entry before we try to use
it.
! * We can skip this in the not-uncommon case that we already had the
same
! * type of lock being requested, since then no one else could have
! * modified the relcache entry in an undesirable way. (In the case
where
! * our own xact modifies the rel, the relcache update happens via
* CommandCounterIncrement, not here.)
*/
if (res != LOCKACQUIRE_ALREADY_HELD)
--- 81,91 ----
/*
* Now that we have the lock, check for invalidation messages, so that
we
* will update or flush any stale relcache entry before we try to use
it.
! * RangeVarLockRelid() specifically relies on us for this. We can skip
! * this in the not-uncommon case that we already had the same type of
lock
! * being requested, since then no one else could have modified the
! * relcache entry in an undesirable way. (In the case where our own
xact
! * modifies the rel, the relcache update happens via
* CommandCounterIncrement, not here.)
*/
if (res != LOCKACQUIRE_ALREADY_HELD)
diff --git a/src/include/catalog/namesindex 7e1e194..da1ddfd 100644
*** a/src/include/catalog/namespace.h
--- b/src/include/catalog/namespace.h
***************
*** 15,20 ****
--- 15,21 ----
#define NAMESPACE_H
#include "nodes/primnodes.h"
+ #include "storage/lock.h"
/*
***************
*** 48,53 **** typedef struct OverrideSearchPath
--- 49,56 ----
extern Oid RangeVarGetRelid(const RangeVar *relation, bool failOK);
+ extern Oid RangeVarLockRelid(const RangeVar *relation, LOCKMODE lockmode,
+ bool failOK);
extern Oid RangeVarGetCreationNamespace(const RangeVar *newRelation);
extern Oid RangeVarGetAndCheckCreationNamespace(const RangeVar
*newRelation);
extern void RangeVarAdjustRelationPersistence(RangeVar *newRelation, Oid
nspid);
diff --git a/src/include/storage/sinvaindex e9ce025..aba474d 100644
*** a/src/include/storage/sinval.h
--- b/src/include/storage/sinval.h
***************
*** 116,121 **** typedef union
--- 116,125 ----
} SharedInvalidationMessage;
+ /* Counter of messages processed; don't worry about overflow. */
+ extern uint64 SharedInvalidMessageCounter;
+
+
extern void SendSharedInvalidMessages(const SharedInvalidationMessage *msgs,
int n);
extern void ReceiveSharedInvalidMessages(
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