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/*-------------------------------------------------------------------------
*
* evtcache.c
* Special-purpose cache for event trigger data.
*
* Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* src/backend/utils/cache/evtcache.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/genam.h"
#include "access/heapam.h"
#include "catalog/pg_event_trigger.h"
#include "catalog/indexing.h"
#include "catalog/pg_type.h"
#include "commands/trigger.h"
#include "utils/array.h"
#include "utils/builtins.h"
#include "utils/evtcache.h"
#include "utils/inval.h"
#include "utils/memutils.h"
#include "utils/hsearch.h"
#include "utils/rel.h"
#include "utils/snapmgr.h"
#include "utils/syscache.h"
typedef struct
{
EventTriggerEvent event;
List *triggerlist;
} EventTriggerCacheEntry;
static HTAB *EventTriggerCache;
static MemoryContext EventTriggerCacheContext;
static void BuildEventTriggerCache(void);
static void InvalidateEventCacheCallback(Datum arg,
int cacheid, uint32 hashvalue);
static int DecodeTextArrayToCString(Datum array, char ***cstringp);
/*
* Search the event cache by trigger event.
*
* Note that the caller had better copy any data it wants to keep around
* across any operation that might touch a system catalog into some other
* memory context, since a cache reset could blow the return value away.
*/
List *
EventCacheLookup(EventTriggerEvent event)
{
EventTriggerCacheEntry *entry;
if (EventTriggerCache == NULL)
BuildEventTriggerCache();
entry = hash_search(EventTriggerCache, &event, HASH_FIND, NULL);
return entry != NULL ? entry->triggerlist : NULL;
}
/*
* Rebuild the event trigger cache.
*/
static void
BuildEventTriggerCache(void)
{
HASHCTL ctl;
HTAB *cache;
MemoryContext oldcontext;
Relation rel;
Relation irel;
SysScanDesc scan;
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.
*/
MemoryContextReset(EventTriggerCacheContext);
}
else
{
/*
* This is our first time attempting to build the cache, so we need
* to set up the memory context and register a syscache callback to
* capture future invalidation events.
*/
if (CacheMemoryContext == NULL)
CreateCacheMemoryContext();
EventTriggerCacheContext =
AllocSetContextCreate(CacheMemoryContext,
"EventTriggerCache",
ALLOCSET_DEFAULT_MINSIZE,
ALLOCSET_DEFAULT_INITSIZE,
ALLOCSET_DEFAULT_MAXSIZE);
CacheRegisterSyscacheCallback(EVENTTRIGGEROID,
InvalidateEventCacheCallback,
(Datum) 0);
}
/* 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.
*/
MemSet(&ctl, 0, sizeof(ctl));
ctl.keysize = sizeof(EventTriggerEvent);
ctl.entrysize = sizeof(EventTriggerCacheEntry);
ctl.hash = tag_hash;
cache = hash_create("Event Trigger Cache", 32, &ctl,
HASH_ELEM | HASH_FUNCTION);
/*
* Prepare to scan pg_event_trigger in name order. We use an MVCC
* snapshot to avoid getting inconsistent results if the table is
* being concurrently updated.
*/
rel = relation_open(EventTriggerRelationId, AccessShareLock);
irel = index_open(EventTriggerNameIndexId, AccessShareLock);
scan = systable_beginscan_ordered(rel, irel, GetLatestSnapshot(), 0, NULL);
/*
* Build a cache item for each pg_event_trigger tuple, and append each
* one to the appropriate cache entry.
*/
for (;;)
{
HeapTuple tup;
Form_pg_event_trigger form;
char *evtevent;
EventTriggerEvent event;
EventTriggerCacheItem *item;
Datum evttags;
bool evttags_isnull;
EventTriggerCacheEntry *entry;
bool found;
/* Get next tuple. */
tup = systable_getnext_ordered(scan, ForwardScanDirection);
if (!HeapTupleIsValid(tup))
break;
/* Skip trigger if disabled. */
form = (Form_pg_event_trigger) GETSTRUCT(tup);
if (form->evtenabled == TRIGGER_DISABLED)
continue;
/* Decode event name. */
evtevent = NameStr(form->evtevent);
if (strcmp(evtevent, "ddl_command_start") == 0)
event = EVT_DDLCommandStart;
else
continue;
/* Allocate new cache item. */
item = palloc0(sizeof(EventTriggerCacheItem));
item->fnoid = form->evtfoid;
item->enabled = form->evtenabled;
/* Decode and sort tags array. */
evttags = heap_getattr(tup, Anum_pg_event_trigger_evttags,
RelationGetDescr(rel), &evttags_isnull);
if (!evttags_isnull)
{
item->ntags = DecodeTextArrayToCString(evttags, &item->tag);
qsort(item->tag, item->ntags, sizeof(char *), pg_qsort_strcmp);
}
/* Add to cache entry. */
entry = hash_search(cache, &event, HASH_ENTER, &found);
if (found)
entry->triggerlist = lappend(entry->triggerlist, item);
else
entry->triggerlist = list_make1(item);
}
/* Done with pg_event_trigger scan. */
systable_endscan_ordered(scan);
index_close(irel, AccessShareLock);
relation_close(rel, AccessShareLock);
/* Restore previous memory context. */
MemoryContextSwitchTo(oldcontext);
/* Cache is now valid. */
EventTriggerCache = cache;
}
/*
* Decode text[] to an array of C strings.
*
* We could avoid a bit of overhead here if we were willing to duplicate some
* of the logic from deconstruct_array, but it doesn't seem worth the code
* complexity.
*/
static int
DecodeTextArrayToCString(Datum array, char ***cstringp)
{
ArrayType *arr = DatumGetArrayTypeP(array);
Datum *elems;
char **cstring;
int i;
int nelems;
if (ARR_NDIM(arr) != 1 || ARR_HASNULL(arr) || ARR_ELEMTYPE(arr) != TEXTOID)
elog(ERROR, "expected 1-D text array");
deconstruct_array(arr, TEXTOID, -1, false, 'i', &elems, NULL, &nelems);
cstring = palloc(nelems * sizeof(char *));
for (i = 0; i < nelems; ++i)
cstring[i] = TextDatumGetCString(elems[i]);
pfree(elems);
*cstringp = cstring;
return nelems;
}
/*
* Flush all cache entries when pg_event_trigger is updated.
*
* This should be rare enough that we don't need to be very granular about
* it, so we just blow away everything, which also avoids the possibility of
* memory leaks.
*/
static void
InvalidateEventCacheCallback(Datum arg, int cacheid, uint32 hashvalue)
{
MemoryContextReset(EventTriggerCacheContext);
EventTriggerCache = NULL;
}
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