rdelaage
/
postgresql
mirror of https://git.postgresql.org/git/postgresql.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

Fix cache flush hazard in event trigger cache. 

Bug spotted by Jeff Davis using -DCLOBBER_CACHE_ALWAYS.
This commit is contained in:
Robert Haas 2012-08-08 16:38:37 -04:00
parent 2751740ab5
commit 21786db81f
1 changed files with 39 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

55
src/backend/utils/cache/evtcache.c vendored
View File

@ -29,6 +29,13 @@
#include "utils/snapmgr.h"
#include "utils/syscache.h"
typedef enum
{
ETCS_NEEDS_REBUILD,
ETCS_REBUILD_STARTED,
ETCS_VALID
} EventTriggerCacheStateType;
typedef struct
{
EventTriggerEvent event;
@ -37,6 +44,7 @@ typedef struct
static HTAB *EventTriggerCache;
static MemoryContext EventTriggerCacheContext;
static EventTriggerCacheStateType EventTriggerCacheState = ETCS_NEEDS_REBUILD;
static void BuildEventTriggerCache(void);
static void InvalidateEventCacheCallback(Datum arg,
@ -55,7 +63,7 @@ EventCacheLookup(EventTriggerEvent event)
{
EventTriggerCacheEntry *entry;
if (EventTriggerCache == NULL)
if (EventTriggerCacheState != ETCS_VALID)
BuildEventTriggerCache();
entry = hash_search(EventTriggerCache, &event, HASH_FIND, NULL);
return entry != NULL ? entry->triggerlist : NULL;
@ -77,12 +85,9 @@ BuildEventTriggerCache(void)
if (EventTriggerCacheContext != NULL)
{
/*
* The cache has been previously built, and subsequently invalidated,
* and now we're trying to rebuild it. Normally, there won't be
* anything in the context at this point, because the invalidation
* will have already reset it. But if the previous attempt to rebuild
* the cache failed, then there might be some junk lying around
* that we want to reclaim.
* Free up any memory already allocated in EventTriggerCacheContext.
* This can happen either because a previous rebuild failed, or
* because an invalidation happened before the rebuild was complete.
*/
MemoryContextResetAndDeleteChildren(EventTriggerCacheContext);
}
@ -109,12 +114,10 @@ BuildEventTriggerCache(void)
/* Switch to correct memory context. */
oldcontext = MemoryContextSwitchTo(EventTriggerCacheContext);
/*
* Create a new hash table, but don't assign it to the global variable
* until it accurately represents the state of the catalogs, so that
* if we fail midway through this we won't end up with incorrect cache
* contents.
*/
/* Prevent the memory context from being nuked while we're rebuilding. */
EventTriggerCacheState = ETCS_REBUILD_STARTED;
/* Create new hash table. */
MemSet(&ctl, 0, sizeof(ctl));
ctl.keysize = sizeof(EventTriggerEvent);
ctl.entrysize = sizeof(EventTriggerCacheEntry);
@ -195,8 +198,17 @@ BuildEventTriggerCache(void)
/* Restore previous memory context. */
MemoryContextSwitchTo(oldcontext);
/* Cache is now valid. */
/* Install new cache. */
EventTriggerCache = cache;
/*
* If the cache has been invalidated since we entered this routine, we
* still use and return the cache we just finished constructing, to avoid
* infinite loops, but we leave the cache marked stale so that we'll
* rebuild it again on next access. Otherwise, we mark the cache valid.
*/
if (EventTriggerCacheState == ETCS_REBUILD_STARTED)
EventTriggerCacheState = ETCS_VALID;
}
/*
@ -238,6 +250,17 @@ DecodeTextArrayToCString(Datum array, char ***cstringp)
static void
InvalidateEventCacheCallback(Datum arg, int cacheid, uint32 hashvalue)
{
MemoryContextResetAndDeleteChildren(EventTriggerCacheContext);
EventTriggerCache = NULL;
/*
* If the cache isn't valid, then there might be a rebuild in progress,
* so we can't immediately blow it away. But it's advantageous to do
* this when possible, so as to immediately free memory.
*/
if (EventTriggerCacheState == ETCS_VALID)
{
MemoryContextResetAndDeleteChildren(EventTriggerCacheContext);
EventTriggerCache = NULL;
}
/* Mark cache for rebuild. */
EventTriggerCacheState = ETCS_NEEDS_REBUILD;
}