/*
* ShmemInitHash -- Create and initialize, or attach to, a
* shared memory hash table.
*
* We assume caller is doing some kind of synchronization
* so that two people don't try to create/initialize the
* table at once.
*
* max_size is the estimated maximum number of hashtable entries. This is
* not a hard limit, but the access efficiency will degrade if it is
* exceeded substantially (since it's used to compute directory size and
* the hash table buckets will get overfull).
*
* init_size is the number of hashtable entries to preallocate. For a table
* whose maximum size is certain, this should be equal to max_size; that
* ensures that no run-time out-of-shared-memory failures can occur.
*/
HTAB *
ShmemInitHash(const char *name, /* table string name for shmem index */
long init_size, /* initial table size */
long max_size, /* max size of the table */
HASHCTL *infoP, /* info about key and bucket size */
int hash_flags) /* info about infoP */
{
bool found;
void *location;
/*
* Hash tables allocated in shared memory have a fixed directory; it can't
* grow or other backends wouldn't be able to find it. So, make sure we
* make it big enough to start with.
*
* The shared memory allocator must be specified too.
*/
infoP->dsize = infoP->max_dsize = hash_select_dirsize(max_size);
infoP->alloc = ShmemAlloc;
hash_flags |= HASH_SHARED_MEM | HASH_ALLOC | HASH_DIRSIZE;
/* look it up in the shmem index */
location = ShmemInitStruct(name,
hash_get_shared_size(infoP, hash_flags),
&found);
/*
* If fail, shmem index is corrupted. Let caller give the error message
* since it has more information
*/
if (location == NULL)
return NULL;
/*
* if it already exists, attach to it rather than allocate and initialize
* new space
*/
if (found)
hash_flags |= HASH_ATTACH;
/* Pass location of hashtable header to hash_create */
infoP->hctl = (HASHHDR *) location;
return hash_create(name, init_size, infoP, hash_flags);
}
/*
* ShmemInitHash -- Create and initialize, or attach to, a
* shared memory hash table.
*
* We assume caller is doing some kind of synchronization
* so that two processes don't try to create/initialize the same
* table at once. (In practice, all creations are done in the postmaster
* process; child processes should always be attaching to existing tables.)
*
* max_size is the estimated maximum number of hashtable entries. This is
* not a hard limit, but the access efficiency will degrade if it is
* exceeded substantially (since it's used to compute directory size and
* the hash table buckets will get overfull).
*
* init_size is the number of hashtable entries to preallocate. For a table
* whose maximum size is certain, this should be equal to max_size; that
* ensures that no run-time out-of-shared-memory failures can occur.
*
* Note: before Postgres 9.0, this function returned NULL for some failure
* cases. Now, it always throws error instead, so callers need not check
* for NULL.
*/
HTAB *
ShmemInitHash(const char *name, /* table string name for shmem index */
long init_size, /* initial table size */
long max_size, /* max size of the table */
HASHCTL *infoP, /* info about key and bucket size */
int hash_flags) /* info about infoP */
{
bool found;
void *location;
/*
* Hash tables allocated in shared memory have a fixed directory; it can't
* grow or other backends wouldn't be able to find it. So, make sure we
* make it big enough to start with.
*
* The shared memory allocator must be specified too.
*/
infoP->dsize = infoP->max_dsize = hash_select_dirsize(max_size);
infoP->alloc = ShmemAlloc;
hash_flags |= HASH_SHARED_MEM | HASH_ALLOC | HASH_DIRSIZE;
/* look it up in the shmem index */
location = ShmemInitStruct(name,
hash_get_shared_size(infoP, hash_flags),
&found);
/*
* if it already exists, attach to it rather than allocate and initialize
* new space
*/
if (found)
hash_flags |= HASH_ATTACH;
if(strcmp(name, "block lsn") == 0 || strcmp(name, "relation last block") == 0) {
ereport(WARNING,
(errmsg("%s: %c", name, found+'0')));
}
/* Pass location of hashtable header to hash_create */
infoP->hctl = (HASHHDR *) location;
return hash_create(name, init_size, infoP, hash_flags);
}
