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/*-------------------------------------------------------------------------
*
* attoptcache.c
* Attribute options cache management.
*
* Attribute options are cached separately from the fixed-size portion of
* pg_attribute entries, which are handled by the relcache.
*
* Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* src/backend/utils/cache/attoptcache.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/reloptions.h"
#include "utils/attoptcache.h"
#include "utils/catcache.h"
#include "utils/hsearch.h"
#include "utils/inval.h"
#include "utils/syscache.h"
/* Hash table for informations about each attribute's options */
static HTAB *AttoptCacheHash = NULL;
/* attrelid and attnum form the lookup key, and must appear first */
typedef struct
{
Oid attrelid;
int attnum;
} AttoptCacheKey;
typedef struct
{
AttoptCacheKey key; /* lookup key - must be first */
AttributeOpts *opts; /* options, or NULL if none */
} AttoptCacheEntry;
/*
* InvalidateAttoptCacheCallback
* Flush all cache entries when pg_attribute is updated.
*
* When pg_attribute is updated, we must flush the cache entry at least
* for that attribute. Currently, we just flush them all. Since attribute
* options are not currently used in performance-critical paths (such as
* query execution), this seems OK.
*/
static void
InvalidateAttoptCacheCallback(Datum arg, int cacheid, uint32 hashvalue)
{
HASH_SEQ_STATUS status;
AttoptCacheEntry *attopt;
hash_seq_init(&status, AttoptCacheHash);
while ((attopt = (AttoptCacheEntry *) hash_seq_search(&status)) != NULL)
{
if (attopt->opts)
pfree(attopt->opts);
if (hash_search(AttoptCacheHash,
(void *) &attopt->key,
HASH_REMOVE,
NULL) == NULL)
elog(ERROR, "hash table corrupted");
}
}
/*
* InitializeAttoptCache
* Initialize the tablespace cache.
*/
static void
InitializeAttoptCache(void)
{
HASHCTL ctl;
/* Initialize the hash table. */
MemSet(&ctl, 0, sizeof(ctl));
ctl.keysize = sizeof(AttoptCacheKey);
ctl.entrysize = sizeof(AttoptCacheEntry);
ctl.hash = tag_hash;
AttoptCacheHash =
hash_create("Attopt cache", 256, &ctl,
HASH_ELEM | HASH_FUNCTION);
/* Make sure we've initialized CacheMemoryContext. */
if (!CacheMemoryContext)
CreateCacheMemoryContext();
/* Watch for invalidation events. */
CacheRegisterSyscacheCallback(ATTNUM,
InvalidateAttoptCacheCallback,
(Datum) 0);
}
/*
* get_attribute_options
* Fetch attribute options for a specified table OID.
*/
AttributeOpts *
get_attribute_options(Oid attrelid, int attnum)
{
AttoptCacheKey key;
AttoptCacheEntry *attopt;
AttributeOpts *result;
HeapTuple tp;
/* Find existing cache entry, if any. */
if (!AttoptCacheHash)
InitializeAttoptCache();
memset(&key, 0, sizeof(key)); /* make sure any padding bits are
* unset */
key.attrelid = attrelid;
key.attnum = attnum;
attopt =
(AttoptCacheEntry *) hash_search(AttoptCacheHash,
(void *) &key,
HASH_FIND,
NULL);
/* Not found in Attopt cache. Construct new cache entry. */
if (!attopt)
{
AttributeOpts *opts;
tp = SearchSysCache2(ATTNUM,
ObjectIdGetDatum(attrelid),
Int16GetDatum(attnum));
/*
* If we don't find a valid HeapTuple, it must mean someone has
* managed to request attribute details for a non-existent attribute.
* We treat that case as if no options were specified.
*/
if (!HeapTupleIsValid(tp))
opts = NULL;
else
{
Datum datum;
bool isNull;
datum = SysCacheGetAttr(ATTNUM,
tp,
Anum_pg_attribute_attoptions,
&isNull);
if (isNull)
opts = NULL;
else
{
bytea *bytea_opts = attribute_reloptions(datum, false);
opts = MemoryContextAlloc(CacheMemoryContext,
VARSIZE(bytea_opts));
memcpy(opts, bytea_opts, VARSIZE(bytea_opts));
}
ReleaseSysCache(tp);
}
/*
* It's important to create the actual cache entry only after reading
* pg_attribute, since the read could cause a cache flush.
*/
attopt = (AttoptCacheEntry *) hash_search(AttoptCacheHash,
(void *) &key,
HASH_ENTER,
NULL);
attopt->opts = opts;
}
/* Return results in caller's memory context. */
if (attopt->opts == NULL)
return NULL;
result = palloc(VARSIZE(attopt->opts));
memcpy(result, attopt->opts, VARSIZE(attopt->opts));
return result;
}
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