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1529 lines
43 KiB
C
1529 lines
43 KiB
C
/*-------------------------------------------------------------------------
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*
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* dynahash.c
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* dynamic hash tables
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*
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* dynahash.c supports both local-to-a-backend hash tables and hash tables in
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* shared memory. For shared hash tables, it is the caller's responsibility
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* to provide appropriate access interlocking. The simplest convention is
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* that a single LWLock protects the whole hash table. Searches (HASH_FIND or
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* hash_seq_search) need only shared lock, but any update requires exclusive
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* lock. For heavily-used shared tables, the single-lock approach creates a
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* concurrency bottleneck, so we also support "partitioned" locking wherein
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* there are multiple LWLocks guarding distinct subsets of the table. To use
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* a hash table in partitioned mode, the HASH_PARTITION flag must be given
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* to hash_create. This prevents any attempt to split buckets on-the-fly.
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* Therefore, each hash bucket chain operates independently, and no fields
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* of the hash header change after init except nentries and freeList.
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* A partitioned table uses a spinlock to guard changes of those two fields.
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* This lets any subset of the hash buckets be treated as a separately
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* lockable partition. We expect callers to use the low-order bits of a
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* lookup key's hash value as a partition number --- this will work because
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* of the way calc_bucket() maps hash values to bucket numbers.
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*
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* Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/utils/hash/dynahash.c,v 1.80 2010/01/02 16:57:56 momjian Exp $
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*
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*-------------------------------------------------------------------------
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*/
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/*
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* Original comments:
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*
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* Dynamic hashing, after CACM April 1988 pp 446-457, by Per-Ake Larson.
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* Coded into C, with minor code improvements, and with hsearch(3) interface,
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* by ejp@ausmelb.oz, Jul 26, 1988: 13:16;
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* also, hcreate/hdestroy routines added to simulate hsearch(3).
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*
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* These routines simulate hsearch(3) and family, with the important
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* difference that the hash table is dynamic - can grow indefinitely
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* beyond its original size (as supplied to hcreate()).
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*
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* Performance appears to be comparable to that of hsearch(3).
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* The 'source-code' options referred to in hsearch(3)'s 'man' page
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* are not implemented; otherwise functionality is identical.
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*
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* Compilation controls:
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* DEBUG controls some informative traces, mainly for debugging.
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* HASH_STATISTICS causes HashAccesses and HashCollisions to be maintained;
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* when combined with HASH_DEBUG, these are displayed by hdestroy().
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*
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* Problems & fixes to ejp@ausmelb.oz. WARNING: relies on pre-processor
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* concatenation property, in probably unnecessary code 'optimisation'.
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*
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* Modified margo@postgres.berkeley.edu February 1990
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* added multiple table interface
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* Modified by sullivan@postgres.berkeley.edu April 1990
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* changed ctl structure for shared memory
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*/
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#include "postgres.h"
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#include "access/xact.h"
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#include "storage/shmem.h"
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#include "storage/spin.h"
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#include "utils/dynahash.h"
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#include "utils/memutils.h"
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/*
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* Constants
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*
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* A hash table has a top-level "directory", each of whose entries points
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* to a "segment" of ssize bucket headers. The maximum number of hash
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* buckets is thus dsize * ssize (but dsize may be expansible). Of course,
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* the number of records in the table can be larger, but we don't want a
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* whole lot of records per bucket or performance goes down.
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*
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* In a hash table allocated in shared memory, the directory cannot be
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* expanded because it must stay at a fixed address. The directory size
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* should be selected using hash_select_dirsize (and you'd better have
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* a good idea of the maximum number of entries!). For non-shared hash
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* tables, the initial directory size can be left at the default.
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*/
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#define DEF_SEGSIZE 256
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#define DEF_SEGSIZE_SHIFT 8 /* must be log2(DEF_SEGSIZE) */
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#define DEF_DIRSIZE 256
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#define DEF_FFACTOR 1 /* default fill factor */
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/* A hash bucket is a linked list of HASHELEMENTs */
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typedef HASHELEMENT *HASHBUCKET;
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/* A hash segment is an array of bucket headers */
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typedef HASHBUCKET *HASHSEGMENT;
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/*
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* Header structure for a hash table --- contains all changeable info
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*
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* In a shared-memory hash table, the HASHHDR is in shared memory, while
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* each backend has a local HTAB struct. For a non-shared table, there isn't
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* any functional difference between HASHHDR and HTAB, but we separate them
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* anyway to share code between shared and non-shared tables.
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*/
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struct HASHHDR
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{
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/* In a partitioned table, take this lock to touch nentries or freeList */
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slock_t mutex; /* unused if not partitioned table */
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/* These fields change during entry addition/deletion */
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long nentries; /* number of entries in hash table */
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HASHELEMENT *freeList; /* linked list of free elements */
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/* These fields can change, but not in a partitioned table */
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/* Also, dsize can't change in a shared table, even if unpartitioned */
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long dsize; /* directory size */
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long nsegs; /* number of allocated segments (<= dsize) */
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uint32 max_bucket; /* ID of maximum bucket in use */
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uint32 high_mask; /* mask to modulo into entire table */
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uint32 low_mask; /* mask to modulo into lower half of table */
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/* These fields are fixed at hashtable creation */
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Size keysize; /* hash key length in bytes */
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Size entrysize; /* total user element size in bytes */
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long num_partitions; /* # partitions (must be power of 2), or 0 */
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long ffactor; /* target fill factor */
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long max_dsize; /* 'dsize' limit if directory is fixed size */
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long ssize; /* segment size --- must be power of 2 */
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int sshift; /* segment shift = log2(ssize) */
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int nelem_alloc; /* number of entries to allocate at once */
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#ifdef HASH_STATISTICS
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/*
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* Count statistics here. NB: stats code doesn't bother with mutex, so
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* counts could be corrupted a bit in a partitioned table.
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*/
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long accesses;
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long collisions;
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#endif
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};
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#define IS_PARTITIONED(hctl) ((hctl)->num_partitions != 0)
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/*
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* Top control structure for a hashtable --- in a shared table, each backend
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* has its own copy (OK since no fields change at runtime)
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*/
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struct HTAB
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{
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HASHHDR *hctl; /* => shared control information */
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HASHSEGMENT *dir; /* directory of segment starts */
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HashValueFunc hash; /* hash function */
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HashCompareFunc match; /* key comparison function */
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HashCopyFunc keycopy; /* key copying function */
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HashAllocFunc alloc; /* memory allocator */
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MemoryContext hcxt; /* memory context if default allocator used */
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char *tabname; /* table name (for error messages) */
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bool isshared; /* true if table is in shared memory */
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/* freezing a shared table isn't allowed, so we can keep state here */
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bool frozen; /* true = no more inserts allowed */
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/* We keep local copies of these fixed values to reduce contention */
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Size keysize; /* hash key length in bytes */
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long ssize; /* segment size --- must be power of 2 */
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int sshift; /* segment shift = log2(ssize) */
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};
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/*
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* Key (also entry) part of a HASHELEMENT
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*/
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#define ELEMENTKEY(helem) (((char *)(helem)) + MAXALIGN(sizeof(HASHELEMENT)))
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/*
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* Fast MOD arithmetic, assuming that y is a power of 2 !
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*/
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#define MOD(x,y) ((x) & ((y)-1))
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#if HASH_STATISTICS
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static long hash_accesses,
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hash_collisions,
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hash_expansions;
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#endif
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/*
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* Private function prototypes
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*/
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static void *DynaHashAlloc(Size size);
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static HASHSEGMENT seg_alloc(HTAB *hashp);
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static bool element_alloc(HTAB *hashp, int nelem);
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static bool dir_realloc(HTAB *hashp);
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static bool expand_table(HTAB *hashp);
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static HASHBUCKET get_hash_entry(HTAB *hashp);
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static void hdefault(HTAB *hashp);
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static int choose_nelem_alloc(Size entrysize);
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static bool init_htab(HTAB *hashp, long nelem);
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static void hash_corrupted(HTAB *hashp);
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static void register_seq_scan(HTAB *hashp);
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static void deregister_seq_scan(HTAB *hashp);
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static bool has_seq_scans(HTAB *hashp);
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/*
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* memory allocation support
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*/
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static MemoryContext CurrentDynaHashCxt = NULL;
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static void *
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DynaHashAlloc(Size size)
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{
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Assert(MemoryContextIsValid(CurrentDynaHashCxt));
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return MemoryContextAlloc(CurrentDynaHashCxt, size);
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}
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/*
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* HashCompareFunc for string keys
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*
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* Because we copy keys with strlcpy(), they will be truncated at keysize-1
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* bytes, so we can only compare that many ... hence strncmp is almost but
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* not quite the right thing.
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*/
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static int
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string_compare(const char *key1, const char *key2, Size keysize)
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{
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return strncmp(key1, key2, keysize - 1);
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}
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/************************** CREATE ROUTINES **********************/
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/*
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* hash_create -- create a new dynamic hash table
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*
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* tabname: a name for the table (for debugging purposes)
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* nelem: maximum number of elements expected
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* *info: additional table parameters, as indicated by flags
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* flags: bitmask indicating which parameters to take from *info
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*
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* Note: for a shared-memory hashtable, nelem needs to be a pretty good
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* estimate, since we can't expand the table on the fly. But an unshared
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* hashtable can be expanded on-the-fly, so it's better for nelem to be
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* on the small side and let the table grow if it's exceeded. An overly
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* large nelem will penalize hash_seq_search speed without buying much.
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*/
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HTAB *
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hash_create(const char *tabname, long nelem, HASHCTL *info, int flags)
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{
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HTAB *hashp;
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HASHHDR *hctl;
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/*
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* For shared hash tables, we have a local hash header (HTAB struct) that
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* we allocate in TopMemoryContext; all else is in shared memory.
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*
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* For non-shared hash tables, everything including the hash header is in
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* a memory context created specially for the hash table --- this makes
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* hash_destroy very simple. The memory context is made a child of either
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* a context specified by the caller, or TopMemoryContext if nothing is
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* specified.
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*/
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if (flags & HASH_SHARED_MEM)
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{
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/* Set up to allocate the hash header */
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CurrentDynaHashCxt = TopMemoryContext;
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}
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else
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{
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/* Create the hash table's private memory context */
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if (flags & HASH_CONTEXT)
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CurrentDynaHashCxt = info->hcxt;
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else
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CurrentDynaHashCxt = TopMemoryContext;
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CurrentDynaHashCxt = AllocSetContextCreate(CurrentDynaHashCxt,
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tabname,
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ALLOCSET_DEFAULT_MINSIZE,
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ALLOCSET_DEFAULT_INITSIZE,
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ALLOCSET_DEFAULT_MAXSIZE);
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}
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/* Initialize the hash header, plus a copy of the table name */
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hashp = (HTAB *) DynaHashAlloc(sizeof(HTAB) + strlen(tabname) +1);
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MemSet(hashp, 0, sizeof(HTAB));
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hashp->tabname = (char *) (hashp + 1);
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strcpy(hashp->tabname, tabname);
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if (flags & HASH_FUNCTION)
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hashp->hash = info->hash;
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else
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hashp->hash = string_hash; /* default hash function */
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/*
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* If you don't specify a match function, it defaults to string_compare if
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* you used string_hash (either explicitly or by default) and to memcmp
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* otherwise. (Prior to PostgreSQL 7.4, memcmp was always used.)
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*/
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if (flags & HASH_COMPARE)
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hashp->match = info->match;
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else if (hashp->hash == string_hash)
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hashp->match = (HashCompareFunc) string_compare;
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else
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hashp->match = memcmp;
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/*
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* Similarly, the key-copying function defaults to strlcpy or memcpy.
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*/
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if (flags & HASH_KEYCOPY)
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hashp->keycopy = info->keycopy;
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else if (hashp->hash == string_hash)
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hashp->keycopy = (HashCopyFunc) strlcpy;
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else
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hashp->keycopy = memcpy;
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if (flags & HASH_ALLOC)
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hashp->alloc = info->alloc;
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else
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hashp->alloc = DynaHashAlloc;
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if (flags & HASH_SHARED_MEM)
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{
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/*
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* ctl structure and directory are preallocated for shared memory
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* tables. Note that HASH_DIRSIZE and HASH_ALLOC had better be set as
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* well.
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*/
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hashp->hctl = info->hctl;
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hashp->dir = (HASHSEGMENT *) (((char *) info->hctl) + sizeof(HASHHDR));
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hashp->hcxt = NULL;
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hashp->isshared = true;
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/* hash table already exists, we're just attaching to it */
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if (flags & HASH_ATTACH)
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{
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/* make local copies of some heavily-used values */
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hctl = hashp->hctl;
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hashp->keysize = hctl->keysize;
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hashp->ssize = hctl->ssize;
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hashp->sshift = hctl->sshift;
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return hashp;
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}
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}
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else
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{
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/* setup hash table defaults */
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hashp->hctl = NULL;
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hashp->dir = NULL;
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hashp->hcxt = CurrentDynaHashCxt;
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hashp->isshared = false;
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}
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if (!hashp->hctl)
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{
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hashp->hctl = (HASHHDR *) hashp->alloc(sizeof(HASHHDR));
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if (!hashp->hctl)
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ereport(ERROR,
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(errcode(ERRCODE_OUT_OF_MEMORY),
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errmsg("out of memory")));
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}
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hashp->frozen = false;
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hdefault(hashp);
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hctl = hashp->hctl;
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if (flags & HASH_PARTITION)
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{
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/* Doesn't make sense to partition a local hash table */
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Assert(flags & HASH_SHARED_MEM);
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/* # of partitions had better be a power of 2 */
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Assert(info->num_partitions == (1L << my_log2(info->num_partitions)));
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hctl->num_partitions = info->num_partitions;
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}
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if (flags & HASH_SEGMENT)
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{
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hctl->ssize = info->ssize;
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hctl->sshift = my_log2(info->ssize);
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/* ssize had better be a power of 2 */
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Assert(hctl->ssize == (1L << hctl->sshift));
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}
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if (flags & HASH_FFACTOR)
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hctl->ffactor = info->ffactor;
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/*
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* SHM hash tables have fixed directory size passed by the caller.
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*/
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if (flags & HASH_DIRSIZE)
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{
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hctl->max_dsize = info->max_dsize;
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hctl->dsize = info->dsize;
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}
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/*
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* hash table now allocates space for key and data but you have to say how
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* much space to allocate
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*/
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if (flags & HASH_ELEM)
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{
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Assert(info->entrysize >= info->keysize);
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hctl->keysize = info->keysize;
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hctl->entrysize = info->entrysize;
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}
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/* make local copies of heavily-used constant fields */
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hashp->keysize = hctl->keysize;
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hashp->ssize = hctl->ssize;
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hashp->sshift = hctl->sshift;
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/* Build the hash directory structure */
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if (!init_htab(hashp, nelem))
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elog(ERROR, "failed to initialize hash table \"%s\"", hashp->tabname);
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/*
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* For a shared hash table, preallocate the requested number of elements.
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* This reduces problems with run-time out-of-shared-memory conditions.
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*
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* For a non-shared hash table, preallocate the requested number of
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* elements if it's less than our chosen nelem_alloc. This avoids wasting
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* space if the caller correctly estimates a small table size.
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*/
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if ((flags & HASH_SHARED_MEM) ||
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nelem < hctl->nelem_alloc)
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{
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if (!element_alloc(hashp, (int) nelem))
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ereport(ERROR,
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(errcode(ERRCODE_OUT_OF_MEMORY),
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errmsg("out of memory")));
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}
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return hashp;
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}
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/*
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* Set default HASHHDR parameters.
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*/
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static void
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hdefault(HTAB *hashp)
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{
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HASHHDR *hctl = hashp->hctl;
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MemSet(hctl, 0, sizeof(HASHHDR));
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hctl->nentries = 0;
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hctl->freeList = NULL;
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hctl->dsize = DEF_DIRSIZE;
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hctl->nsegs = 0;
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/* rather pointless defaults for key & entry size */
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hctl->keysize = sizeof(char *);
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hctl->entrysize = 2 * sizeof(char *);
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hctl->num_partitions = 0; /* not partitioned */
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hctl->ffactor = DEF_FFACTOR;
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/* table has no fixed maximum size */
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hctl->max_dsize = NO_MAX_DSIZE;
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hctl->ssize = DEF_SEGSIZE;
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hctl->sshift = DEF_SEGSIZE_SHIFT;
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#ifdef HASH_STATISTICS
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hctl->accesses = hctl->collisions = 0;
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#endif
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}
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/*
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* Given the user-specified entry size, choose nelem_alloc, ie, how many
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* elements to add to the hash table when we need more.
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*/
|
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static int
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choose_nelem_alloc(Size entrysize)
|
|
{
|
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int nelem_alloc;
|
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Size elementSize;
|
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Size allocSize;
|
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|
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/* Each element has a HASHELEMENT header plus user data. */
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/* NB: this had better match element_alloc() */
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elementSize = MAXALIGN(sizeof(HASHELEMENT)) + MAXALIGN(entrysize);
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/*
|
|
* The idea here is to choose nelem_alloc at least 32, but round up so
|
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* that the allocation request will be a power of 2 or just less. This
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* makes little difference for hash tables in shared memory, but for hash
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* tables managed by palloc, the allocation request will be rounded up to
|
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* a power of 2 anyway. If we fail to take this into account, we'll waste
|
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* as much as half the allocated space.
|
|
*/
|
|
allocSize = 32 * 4; /* assume elementSize at least 8 */
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do
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{
|
|
allocSize <<= 1;
|
|
nelem_alloc = allocSize / elementSize;
|
|
} while (nelem_alloc < 32);
|
|
|
|
return nelem_alloc;
|
|
}
|
|
|
|
/*
|
|
* Compute derived fields of hctl and build the initial directory/segment
|
|
* arrays
|
|
*/
|
|
static bool
|
|
init_htab(HTAB *hashp, long nelem)
|
|
{
|
|
HASHHDR *hctl = hashp->hctl;
|
|
HASHSEGMENT *segp;
|
|
long lnbuckets;
|
|
int nbuckets;
|
|
int nsegs;
|
|
|
|
/*
|
|
* initialize mutex if it's a partitioned table
|
|
*/
|
|
if (IS_PARTITIONED(hctl))
|
|
SpinLockInit(&hctl->mutex);
|
|
|
|
/*
|
|
* Divide number of elements by the fill factor to determine a desired
|
|
* number of buckets. Allocate space for the next greater power of two
|
|
* number of buckets
|
|
*/
|
|
lnbuckets = (nelem - 1) / hctl->ffactor + 1;
|
|
|
|
nbuckets = 1 << my_log2(lnbuckets);
|
|
|
|
/*
|
|
* In a partitioned table, nbuckets must be at least equal to
|
|
* num_partitions; were it less, keys with apparently different partition
|
|
* numbers would map to the same bucket, breaking partition independence.
|
|
* (Normally nbuckets will be much bigger; this is just a safety check.)
|
|
*/
|
|
while (nbuckets < hctl->num_partitions)
|
|
nbuckets <<= 1;
|
|
|
|
hctl->max_bucket = hctl->low_mask = nbuckets - 1;
|
|
hctl->high_mask = (nbuckets << 1) - 1;
|
|
|
|
/*
|
|
* Figure number of directory segments needed, round up to a power of 2
|
|
*/
|
|
nsegs = (nbuckets - 1) / hctl->ssize + 1;
|
|
nsegs = 1 << my_log2(nsegs);
|
|
|
|
/*
|
|
* Make sure directory is big enough. If pre-allocated directory is too
|
|
* small, choke (caller screwed up).
|
|
*/
|
|
if (nsegs > hctl->dsize)
|
|
{
|
|
if (!(hashp->dir))
|
|
hctl->dsize = nsegs;
|
|
else
|
|
return false;
|
|
}
|
|
|
|
/* Allocate a directory */
|
|
if (!(hashp->dir))
|
|
{
|
|
CurrentDynaHashCxt = hashp->hcxt;
|
|
hashp->dir = (HASHSEGMENT *)
|
|
hashp->alloc(hctl->dsize * sizeof(HASHSEGMENT));
|
|
if (!hashp->dir)
|
|
return false;
|
|
}
|
|
|
|
/* Allocate initial segments */
|
|
for (segp = hashp->dir; hctl->nsegs < nsegs; hctl->nsegs++, segp++)
|
|
{
|
|
*segp = seg_alloc(hashp);
|
|
if (*segp == NULL)
|
|
return false;
|
|
}
|
|
|
|
/* Choose number of entries to allocate at a time */
|
|
hctl->nelem_alloc = choose_nelem_alloc(hctl->entrysize);
|
|
|
|
#if HASH_DEBUG
|
|
fprintf(stderr, "init_htab:\n%s%p\n%s%ld\n%s%ld\n%s%d\n%s%ld\n%s%u\n%s%x\n%s%x\n%s%ld\n%s%ld\n",
|
|
"TABLE POINTER ", hashp,
|
|
"DIRECTORY SIZE ", hctl->dsize,
|
|
"SEGMENT SIZE ", hctl->ssize,
|
|
"SEGMENT SHIFT ", hctl->sshift,
|
|
"FILL FACTOR ", hctl->ffactor,
|
|
"MAX BUCKET ", hctl->max_bucket,
|
|
"HIGH MASK ", hctl->high_mask,
|
|
"LOW MASK ", hctl->low_mask,
|
|
"NSEGS ", hctl->nsegs,
|
|
"NENTRIES ", hctl->nentries);
|
|
#endif
|
|
return true;
|
|
}
|
|
|
|
/*
|
|
* Estimate the space needed for a hashtable containing the given number
|
|
* of entries of given size.
|
|
* NOTE: this is used to estimate the footprint of hashtables in shared
|
|
* memory; therefore it does not count HTAB which is in local memory.
|
|
* NB: assumes that all hash structure parameters have default values!
|
|
*/
|
|
Size
|
|
hash_estimate_size(long num_entries, Size entrysize)
|
|
{
|
|
Size size;
|
|
long nBuckets,
|
|
nSegments,
|
|
nDirEntries,
|
|
nElementAllocs,
|
|
elementSize,
|
|
elementAllocCnt;
|
|
|
|
/* estimate number of buckets wanted */
|
|
nBuckets = 1L << my_log2((num_entries - 1) / DEF_FFACTOR + 1);
|
|
/* # of segments needed for nBuckets */
|
|
nSegments = 1L << my_log2((nBuckets - 1) / DEF_SEGSIZE + 1);
|
|
/* directory entries */
|
|
nDirEntries = DEF_DIRSIZE;
|
|
while (nDirEntries < nSegments)
|
|
nDirEntries <<= 1; /* dir_alloc doubles dsize at each call */
|
|
|
|
/* fixed control info */
|
|
size = MAXALIGN(sizeof(HASHHDR)); /* but not HTAB, per above */
|
|
/* directory */
|
|
size = add_size(size, mul_size(nDirEntries, sizeof(HASHSEGMENT)));
|
|
/* segments */
|
|
size = add_size(size, mul_size(nSegments,
|
|
MAXALIGN(DEF_SEGSIZE * sizeof(HASHBUCKET))));
|
|
/* elements --- allocated in groups of choose_nelem_alloc() entries */
|
|
elementAllocCnt = choose_nelem_alloc(entrysize);
|
|
nElementAllocs = (num_entries - 1) / elementAllocCnt + 1;
|
|
elementSize = MAXALIGN(sizeof(HASHELEMENT)) + MAXALIGN(entrysize);
|
|
size = add_size(size,
|
|
mul_size(nElementAllocs,
|
|
mul_size(elementAllocCnt, elementSize)));
|
|
|
|
return size;
|
|
}
|
|
|
|
/*
|
|
* Select an appropriate directory size for a hashtable with the given
|
|
* maximum number of entries.
|
|
* This is only needed for hashtables in shared memory, whose directories
|
|
* cannot be expanded dynamically.
|
|
* NB: assumes that all hash structure parameters have default values!
|
|
*
|
|
* XXX this had better agree with the behavior of init_htab()...
|
|
*/
|
|
long
|
|
hash_select_dirsize(long num_entries)
|
|
{
|
|
long nBuckets,
|
|
nSegments,
|
|
nDirEntries;
|
|
|
|
/* estimate number of buckets wanted */
|
|
nBuckets = 1L << my_log2((num_entries - 1) / DEF_FFACTOR + 1);
|
|
/* # of segments needed for nBuckets */
|
|
nSegments = 1L << my_log2((nBuckets - 1) / DEF_SEGSIZE + 1);
|
|
/* directory entries */
|
|
nDirEntries = DEF_DIRSIZE;
|
|
while (nDirEntries < nSegments)
|
|
nDirEntries <<= 1; /* dir_alloc doubles dsize at each call */
|
|
|
|
return nDirEntries;
|
|
}
|
|
|
|
/*
|
|
* Compute the required initial memory allocation for a shared-memory
|
|
* hashtable with the given parameters. We need space for the HASHHDR
|
|
* and for the (non expansible) directory.
|
|
*/
|
|
Size
|
|
hash_get_shared_size(HASHCTL *info, int flags)
|
|
{
|
|
Assert(flags & HASH_DIRSIZE);
|
|
Assert(info->dsize == info->max_dsize);
|
|
return sizeof(HASHHDR) + info->dsize * sizeof(HASHSEGMENT);
|
|
}
|
|
|
|
|
|
/********************** DESTROY ROUTINES ************************/
|
|
|
|
void
|
|
hash_destroy(HTAB *hashp)
|
|
{
|
|
if (hashp != NULL)
|
|
{
|
|
/* allocation method must be one we know how to free, too */
|
|
Assert(hashp->alloc == DynaHashAlloc);
|
|
/* so this hashtable must have it's own context */
|
|
Assert(hashp->hcxt != NULL);
|
|
|
|
hash_stats("destroy", hashp);
|
|
|
|
/*
|
|
* Free everything by destroying the hash table's memory context.
|
|
*/
|
|
MemoryContextDelete(hashp->hcxt);
|
|
}
|
|
}
|
|
|
|
void
|
|
hash_stats(const char *where, HTAB *hashp)
|
|
{
|
|
#if HASH_STATISTICS
|
|
fprintf(stderr, "%s: this HTAB -- accesses %ld collisions %ld\n",
|
|
where, hashp->hctl->accesses, hashp->hctl->collisions);
|
|
|
|
fprintf(stderr, "hash_stats: entries %ld keysize %ld maxp %u segmentcount %ld\n",
|
|
hashp->hctl->nentries, (long) hashp->hctl->keysize,
|
|
hashp->hctl->max_bucket, hashp->hctl->nsegs);
|
|
fprintf(stderr, "%s: total accesses %ld total collisions %ld\n",
|
|
where, hash_accesses, hash_collisions);
|
|
fprintf(stderr, "hash_stats: total expansions %ld\n",
|
|
hash_expansions);
|
|
#endif
|
|
}
|
|
|
|
/*******************************SEARCH ROUTINES *****************************/
|
|
|
|
|
|
/*
|
|
* get_hash_value -- exported routine to calculate a key's hash value
|
|
*
|
|
* We export this because for partitioned tables, callers need to compute
|
|
* the partition number (from the low-order bits of the hash value) before
|
|
* searching.
|
|
*/
|
|
uint32
|
|
get_hash_value(HTAB *hashp, const void *keyPtr)
|
|
{
|
|
return hashp->hash(keyPtr, hashp->keysize);
|
|
}
|
|
|
|
/* Convert a hash value to a bucket number */
|
|
static inline uint32
|
|
calc_bucket(HASHHDR *hctl, uint32 hash_val)
|
|
{
|
|
uint32 bucket;
|
|
|
|
bucket = hash_val & hctl->high_mask;
|
|
if (bucket > hctl->max_bucket)
|
|
bucket = bucket & hctl->low_mask;
|
|
|
|
return bucket;
|
|
}
|
|
|
|
/*
|
|
* hash_search -- look up key in table and perform action
|
|
* hash_search_with_hash_value -- same, with key's hash value already computed
|
|
*
|
|
* action is one of:
|
|
* HASH_FIND: look up key in table
|
|
* HASH_ENTER: look up key in table, creating entry if not present
|
|
* HASH_ENTER_NULL: same, but return NULL if out of memory
|
|
* HASH_REMOVE: look up key in table, remove entry if present
|
|
*
|
|
* Return value is a pointer to the element found/entered/removed if any,
|
|
* or NULL if no match was found. (NB: in the case of the REMOVE action,
|
|
* the result is a dangling pointer that shouldn't be dereferenced!)
|
|
*
|
|
* HASH_ENTER will normally ereport a generic "out of memory" error if
|
|
* it is unable to create a new entry. The HASH_ENTER_NULL operation is
|
|
* the same except it will return NULL if out of memory. Note that
|
|
* HASH_ENTER_NULL cannot be used with the default palloc-based allocator,
|
|
* since palloc internally ereports on out-of-memory.
|
|
*
|
|
* If foundPtr isn't NULL, then *foundPtr is set TRUE if we found an
|
|
* existing entry in the table, FALSE otherwise. This is needed in the
|
|
* HASH_ENTER case, but is redundant with the return value otherwise.
|
|
*
|
|
* For hash_search_with_hash_value, the hashvalue parameter must have been
|
|
* calculated with get_hash_value().
|
|
*/
|
|
void *
|
|
hash_search(HTAB *hashp,
|
|
const void *keyPtr,
|
|
HASHACTION action,
|
|
bool *foundPtr)
|
|
{
|
|
return hash_search_with_hash_value(hashp,
|
|
keyPtr,
|
|
hashp->hash(keyPtr, hashp->keysize),
|
|
action,
|
|
foundPtr);
|
|
}
|
|
|
|
void *
|
|
hash_search_with_hash_value(HTAB *hashp,
|
|
const void *keyPtr,
|
|
uint32 hashvalue,
|
|
HASHACTION action,
|
|
bool *foundPtr)
|
|
{
|
|
HASHHDR *hctl = hashp->hctl;
|
|
Size keysize;
|
|
uint32 bucket;
|
|
long segment_num;
|
|
long segment_ndx;
|
|
HASHSEGMENT segp;
|
|
HASHBUCKET currBucket;
|
|
HASHBUCKET *prevBucketPtr;
|
|
HashCompareFunc match;
|
|
|
|
#if HASH_STATISTICS
|
|
hash_accesses++;
|
|
hctl->accesses++;
|
|
#endif
|
|
|
|
/*
|
|
* Do the initial lookup
|
|
*/
|
|
bucket = calc_bucket(hctl, hashvalue);
|
|
|
|
segment_num = bucket >> hashp->sshift;
|
|
segment_ndx = MOD(bucket, hashp->ssize);
|
|
|
|
segp = hashp->dir[segment_num];
|
|
|
|
if (segp == NULL)
|
|
hash_corrupted(hashp);
|
|
|
|
prevBucketPtr = &segp[segment_ndx];
|
|
currBucket = *prevBucketPtr;
|
|
|
|
/*
|
|
* Follow collision chain looking for matching key
|
|
*/
|
|
match = hashp->match; /* save one fetch in inner loop */
|
|
keysize = hashp->keysize; /* ditto */
|
|
|
|
while (currBucket != NULL)
|
|
{
|
|
if (currBucket->hashvalue == hashvalue &&
|
|
match(ELEMENTKEY(currBucket), keyPtr, keysize) == 0)
|
|
break;
|
|
prevBucketPtr = &(currBucket->link);
|
|
currBucket = *prevBucketPtr;
|
|
#if HASH_STATISTICS
|
|
hash_collisions++;
|
|
hctl->collisions++;
|
|
#endif
|
|
}
|
|
|
|
if (foundPtr)
|
|
*foundPtr = (bool) (currBucket != NULL);
|
|
|
|
/*
|
|
* OK, now what?
|
|
*/
|
|
switch (action)
|
|
{
|
|
case HASH_FIND:
|
|
if (currBucket != NULL)
|
|
return (void *) ELEMENTKEY(currBucket);
|
|
return NULL;
|
|
|
|
case HASH_REMOVE:
|
|
if (currBucket != NULL)
|
|
{
|
|
/* use volatile pointer to prevent code rearrangement */
|
|
volatile HASHHDR *hctlv = hctl;
|
|
|
|
/* if partitioned, must lock to touch nentries and freeList */
|
|
if (IS_PARTITIONED(hctlv))
|
|
SpinLockAcquire(&hctlv->mutex);
|
|
|
|
Assert(hctlv->nentries > 0);
|
|
hctlv->nentries--;
|
|
|
|
/* remove record from hash bucket's chain. */
|
|
*prevBucketPtr = currBucket->link;
|
|
|
|
/* add the record to the freelist for this table. */
|
|
currBucket->link = hctlv->freeList;
|
|
hctlv->freeList = currBucket;
|
|
|
|
if (IS_PARTITIONED(hctlv))
|
|
SpinLockRelease(&hctlv->mutex);
|
|
|
|
/*
|
|
* better hope the caller is synchronizing access to this
|
|
* element, because someone else is going to reuse it the next
|
|
* time something is added to the table
|
|
*/
|
|
return (void *) ELEMENTKEY(currBucket);
|
|
}
|
|
return NULL;
|
|
|
|
case HASH_ENTER_NULL:
|
|
/* ENTER_NULL does not work with palloc-based allocator */
|
|
Assert(hashp->alloc != DynaHashAlloc);
|
|
/* FALL THRU */
|
|
|
|
case HASH_ENTER:
|
|
/* Return existing element if found, else create one */
|
|
if (currBucket != NULL)
|
|
return (void *) ELEMENTKEY(currBucket);
|
|
|
|
/* disallow inserts if frozen */
|
|
if (hashp->frozen)
|
|
elog(ERROR, "cannot insert into frozen hashtable \"%s\"",
|
|
hashp->tabname);
|
|
|
|
currBucket = get_hash_entry(hashp);
|
|
if (currBucket == NULL)
|
|
{
|
|
/* out of memory */
|
|
if (action == HASH_ENTER_NULL)
|
|
return NULL;
|
|
/* report a generic message */
|
|
if (hashp->isshared)
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_OUT_OF_MEMORY),
|
|
errmsg("out of shared memory")));
|
|
else
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_OUT_OF_MEMORY),
|
|
errmsg("out of memory")));
|
|
}
|
|
|
|
/* link into hashbucket chain */
|
|
*prevBucketPtr = currBucket;
|
|
currBucket->link = NULL;
|
|
|
|
/* copy key into record */
|
|
currBucket->hashvalue = hashvalue;
|
|
hashp->keycopy(ELEMENTKEY(currBucket), keyPtr, keysize);
|
|
|
|
/* caller is expected to fill the data field on return */
|
|
|
|
/*
|
|
* Check if it is time to split a bucket. Can't split if running
|
|
* in partitioned mode, nor if table is the subject of any active
|
|
* hash_seq_search scans. Strange order of these tests is to try
|
|
* to check cheaper conditions first.
|
|
*/
|
|
if (!IS_PARTITIONED(hctl) &&
|
|
hctl->nentries / (long) (hctl->max_bucket + 1) >= hctl->ffactor &&
|
|
!has_seq_scans(hashp))
|
|
{
|
|
/*
|
|
* NOTE: failure to expand table is not a fatal error, it just
|
|
* means we have to run at higher fill factor than we wanted.
|
|
*/
|
|
expand_table(hashp);
|
|
}
|
|
|
|
return (void *) ELEMENTKEY(currBucket);
|
|
}
|
|
|
|
elog(ERROR, "unrecognized hash action code: %d", (int) action);
|
|
|
|
return NULL; /* keep compiler quiet */
|
|
}
|
|
|
|
/*
|
|
* create a new entry if possible
|
|
*/
|
|
static HASHBUCKET
|
|
get_hash_entry(HTAB *hashp)
|
|
{
|
|
/* use volatile pointer to prevent code rearrangement */
|
|
volatile HASHHDR *hctlv = hashp->hctl;
|
|
HASHBUCKET newElement;
|
|
|
|
for (;;)
|
|
{
|
|
/* if partitioned, must lock to touch nentries and freeList */
|
|
if (IS_PARTITIONED(hctlv))
|
|
SpinLockAcquire(&hctlv->mutex);
|
|
|
|
/* try to get an entry from the freelist */
|
|
newElement = hctlv->freeList;
|
|
if (newElement != NULL)
|
|
break;
|
|
|
|
/* no free elements. allocate another chunk of buckets */
|
|
if (IS_PARTITIONED(hctlv))
|
|
SpinLockRelease(&hctlv->mutex);
|
|
|
|
if (!element_alloc(hashp, hctlv->nelem_alloc))
|
|
{
|
|
/* out of memory */
|
|
return NULL;
|
|
}
|
|
}
|
|
|
|
/* remove entry from freelist, bump nentries */
|
|
hctlv->freeList = newElement->link;
|
|
hctlv->nentries++;
|
|
|
|
if (IS_PARTITIONED(hctlv))
|
|
SpinLockRelease(&hctlv->mutex);
|
|
|
|
return newElement;
|
|
}
|
|
|
|
/*
|
|
* hash_get_num_entries -- get the number of entries in a hashtable
|
|
*/
|
|
long
|
|
hash_get_num_entries(HTAB *hashp)
|
|
{
|
|
/*
|
|
* We currently don't bother with the mutex; it's only sensible to call
|
|
* this function if you've got lock on all partitions of the table.
|
|
*/
|
|
return hashp->hctl->nentries;
|
|
}
|
|
|
|
/*
|
|
* hash_seq_init/_search/_term
|
|
* Sequentially search through hash table and return
|
|
* all the elements one by one, return NULL when no more.
|
|
*
|
|
* hash_seq_term should be called if and only if the scan is abandoned before
|
|
* completion; if hash_seq_search returns NULL then it has already done the
|
|
* end-of-scan cleanup.
|
|
*
|
|
* NOTE: caller may delete the returned element before continuing the scan.
|
|
* However, deleting any other element while the scan is in progress is
|
|
* UNDEFINED (it might be the one that curIndex is pointing at!). Also,
|
|
* if elements are added to the table while the scan is in progress, it is
|
|
* unspecified whether they will be visited by the scan or not.
|
|
*
|
|
* NOTE: it is possible to use hash_seq_init/hash_seq_search without any
|
|
* worry about hash_seq_term cleanup, if the hashtable is first locked against
|
|
* further insertions by calling hash_freeze. This is used by nodeAgg.c,
|
|
* wherein it is inconvenient to track whether a scan is still open, and
|
|
* there's no possibility of further insertions after readout has begun.
|
|
*
|
|
* NOTE: to use this with a partitioned hashtable, caller had better hold
|
|
* at least shared lock on all partitions of the table throughout the scan!
|
|
* We can cope with insertions or deletions by our own backend, but *not*
|
|
* with concurrent insertions or deletions by another.
|
|
*/
|
|
void
|
|
hash_seq_init(HASH_SEQ_STATUS *status, HTAB *hashp)
|
|
{
|
|
status->hashp = hashp;
|
|
status->curBucket = 0;
|
|
status->curEntry = NULL;
|
|
if (!hashp->frozen)
|
|
register_seq_scan(hashp);
|
|
}
|
|
|
|
void *
|
|
hash_seq_search(HASH_SEQ_STATUS *status)
|
|
{
|
|
HTAB *hashp;
|
|
HASHHDR *hctl;
|
|
uint32 max_bucket;
|
|
long ssize;
|
|
long segment_num;
|
|
long segment_ndx;
|
|
HASHSEGMENT segp;
|
|
uint32 curBucket;
|
|
HASHELEMENT *curElem;
|
|
|
|
if ((curElem = status->curEntry) != NULL)
|
|
{
|
|
/* Continuing scan of curBucket... */
|
|
status->curEntry = curElem->link;
|
|
if (status->curEntry == NULL) /* end of this bucket */
|
|
++status->curBucket;
|
|
return (void *) ELEMENTKEY(curElem);
|
|
}
|
|
|
|
/*
|
|
* Search for next nonempty bucket starting at curBucket.
|
|
*/
|
|
curBucket = status->curBucket;
|
|
hashp = status->hashp;
|
|
hctl = hashp->hctl;
|
|
ssize = hashp->ssize;
|
|
max_bucket = hctl->max_bucket;
|
|
|
|
if (curBucket > max_bucket)
|
|
{
|
|
hash_seq_term(status);
|
|
return NULL; /* search is done */
|
|
}
|
|
|
|
/*
|
|
* first find the right segment in the table directory.
|
|
*/
|
|
segment_num = curBucket >> hashp->sshift;
|
|
segment_ndx = MOD(curBucket, ssize);
|
|
|
|
segp = hashp->dir[segment_num];
|
|
|
|
/*
|
|
* Pick up the first item in this bucket's chain. If chain is not empty
|
|
* we can begin searching it. Otherwise we have to advance to find the
|
|
* next nonempty bucket. We try to optimize that case since searching a
|
|
* near-empty hashtable has to iterate this loop a lot.
|
|
*/
|
|
while ((curElem = segp[segment_ndx]) == NULL)
|
|
{
|
|
/* empty bucket, advance to next */
|
|
if (++curBucket > max_bucket)
|
|
{
|
|
status->curBucket = curBucket;
|
|
hash_seq_term(status);
|
|
return NULL; /* search is done */
|
|
}
|
|
if (++segment_ndx >= ssize)
|
|
{
|
|
segment_num++;
|
|
segment_ndx = 0;
|
|
segp = hashp->dir[segment_num];
|
|
}
|
|
}
|
|
|
|
/* Begin scan of curBucket... */
|
|
status->curEntry = curElem->link;
|
|
if (status->curEntry == NULL) /* end of this bucket */
|
|
++curBucket;
|
|
status->curBucket = curBucket;
|
|
return (void *) ELEMENTKEY(curElem);
|
|
}
|
|
|
|
void
|
|
hash_seq_term(HASH_SEQ_STATUS *status)
|
|
{
|
|
if (!status->hashp->frozen)
|
|
deregister_seq_scan(status->hashp);
|
|
}
|
|
|
|
/*
|
|
* hash_freeze
|
|
* Freeze a hashtable against future insertions (deletions are
|
|
* still allowed)
|
|
*
|
|
* The reason for doing this is that by preventing any more bucket splits,
|
|
* we no longer need to worry about registering hash_seq_search scans,
|
|
* and thus caller need not be careful about ensuring hash_seq_term gets
|
|
* called at the right times.
|
|
*
|
|
* Multiple calls to hash_freeze() are allowed, but you can't freeze a table
|
|
* with active scans (since hash_seq_term would then do the wrong thing).
|
|
*/
|
|
void
|
|
hash_freeze(HTAB *hashp)
|
|
{
|
|
if (hashp->isshared)
|
|
elog(ERROR, "cannot freeze shared hashtable \"%s\"", hashp->tabname);
|
|
if (!hashp->frozen && has_seq_scans(hashp))
|
|
elog(ERROR, "cannot freeze hashtable \"%s\" because it has active scans",
|
|
hashp->tabname);
|
|
hashp->frozen = true;
|
|
}
|
|
|
|
|
|
/********************************* UTILITIES ************************/
|
|
|
|
/*
|
|
* Expand the table by adding one more hash bucket.
|
|
*/
|
|
static bool
|
|
expand_table(HTAB *hashp)
|
|
{
|
|
HASHHDR *hctl = hashp->hctl;
|
|
HASHSEGMENT old_seg,
|
|
new_seg;
|
|
long old_bucket,
|
|
new_bucket;
|
|
long new_segnum,
|
|
new_segndx;
|
|
long old_segnum,
|
|
old_segndx;
|
|
HASHBUCKET *oldlink,
|
|
*newlink;
|
|
HASHBUCKET currElement,
|
|
nextElement;
|
|
|
|
Assert(!IS_PARTITIONED(hctl));
|
|
|
|
#ifdef HASH_STATISTICS
|
|
hash_expansions++;
|
|
#endif
|
|
|
|
new_bucket = hctl->max_bucket + 1;
|
|
new_segnum = new_bucket >> hashp->sshift;
|
|
new_segndx = MOD(new_bucket, hashp->ssize);
|
|
|
|
if (new_segnum >= hctl->nsegs)
|
|
{
|
|
/* Allocate new segment if necessary -- could fail if dir full */
|
|
if (new_segnum >= hctl->dsize)
|
|
if (!dir_realloc(hashp))
|
|
return false;
|
|
if (!(hashp->dir[new_segnum] = seg_alloc(hashp)))
|
|
return false;
|
|
hctl->nsegs++;
|
|
}
|
|
|
|
/* OK, we created a new bucket */
|
|
hctl->max_bucket++;
|
|
|
|
/*
|
|
* *Before* changing masks, find old bucket corresponding to same hash
|
|
* values; values in that bucket may need to be relocated to new bucket.
|
|
* Note that new_bucket is certainly larger than low_mask at this point,
|
|
* so we can skip the first step of the regular hash mask calc.
|
|
*/
|
|
old_bucket = (new_bucket & hctl->low_mask);
|
|
|
|
/*
|
|
* If we crossed a power of 2, readjust masks.
|
|
*/
|
|
if ((uint32) new_bucket > hctl->high_mask)
|
|
{
|
|
hctl->low_mask = hctl->high_mask;
|
|
hctl->high_mask = (uint32) new_bucket | hctl->low_mask;
|
|
}
|
|
|
|
/*
|
|
* Relocate records to the new bucket. NOTE: because of the way the hash
|
|
* masking is done in calc_bucket, only one old bucket can need to be
|
|
* split at this point. With a different way of reducing the hash value,
|
|
* that might not be true!
|
|
*/
|
|
old_segnum = old_bucket >> hashp->sshift;
|
|
old_segndx = MOD(old_bucket, hashp->ssize);
|
|
|
|
old_seg = hashp->dir[old_segnum];
|
|
new_seg = hashp->dir[new_segnum];
|
|
|
|
oldlink = &old_seg[old_segndx];
|
|
newlink = &new_seg[new_segndx];
|
|
|
|
for (currElement = *oldlink;
|
|
currElement != NULL;
|
|
currElement = nextElement)
|
|
{
|
|
nextElement = currElement->link;
|
|
if ((long) calc_bucket(hctl, currElement->hashvalue) == old_bucket)
|
|
{
|
|
*oldlink = currElement;
|
|
oldlink = &currElement->link;
|
|
}
|
|
else
|
|
{
|
|
*newlink = currElement;
|
|
newlink = &currElement->link;
|
|
}
|
|
}
|
|
/* don't forget to terminate the rebuilt hash chains... */
|
|
*oldlink = NULL;
|
|
*newlink = NULL;
|
|
|
|
return true;
|
|
}
|
|
|
|
|
|
static bool
|
|
dir_realloc(HTAB *hashp)
|
|
{
|
|
HASHSEGMENT *p;
|
|
HASHSEGMENT *old_p;
|
|
long new_dsize;
|
|
long old_dirsize;
|
|
long new_dirsize;
|
|
|
|
if (hashp->hctl->max_dsize != NO_MAX_DSIZE)
|
|
return false;
|
|
|
|
/* Reallocate directory */
|
|
new_dsize = hashp->hctl->dsize << 1;
|
|
old_dirsize = hashp->hctl->dsize * sizeof(HASHSEGMENT);
|
|
new_dirsize = new_dsize * sizeof(HASHSEGMENT);
|
|
|
|
old_p = hashp->dir;
|
|
CurrentDynaHashCxt = hashp->hcxt;
|
|
p = (HASHSEGMENT *) hashp->alloc((Size) new_dirsize);
|
|
|
|
if (p != NULL)
|
|
{
|
|
memcpy(p, old_p, old_dirsize);
|
|
MemSet(((char *) p) + old_dirsize, 0, new_dirsize - old_dirsize);
|
|
hashp->dir = p;
|
|
hashp->hctl->dsize = new_dsize;
|
|
|
|
/* XXX assume the allocator is palloc, so we know how to free */
|
|
Assert(hashp->alloc == DynaHashAlloc);
|
|
pfree(old_p);
|
|
|
|
return true;
|
|
}
|
|
|
|
return false;
|
|
}
|
|
|
|
|
|
static HASHSEGMENT
|
|
seg_alloc(HTAB *hashp)
|
|
{
|
|
HASHSEGMENT segp;
|
|
|
|
CurrentDynaHashCxt = hashp->hcxt;
|
|
segp = (HASHSEGMENT) hashp->alloc(sizeof(HASHBUCKET) * hashp->ssize);
|
|
|
|
if (!segp)
|
|
return NULL;
|
|
|
|
MemSet(segp, 0, sizeof(HASHBUCKET) * hashp->ssize);
|
|
|
|
return segp;
|
|
}
|
|
|
|
/*
|
|
* allocate some new elements and link them into the free list
|
|
*/
|
|
static bool
|
|
element_alloc(HTAB *hashp, int nelem)
|
|
{
|
|
/* use volatile pointer to prevent code rearrangement */
|
|
volatile HASHHDR *hctlv = hashp->hctl;
|
|
Size elementSize;
|
|
HASHELEMENT *firstElement;
|
|
HASHELEMENT *tmpElement;
|
|
HASHELEMENT *prevElement;
|
|
int i;
|
|
|
|
/* Each element has a HASHELEMENT header plus user data. */
|
|
elementSize = MAXALIGN(sizeof(HASHELEMENT)) + MAXALIGN(hctlv->entrysize);
|
|
|
|
CurrentDynaHashCxt = hashp->hcxt;
|
|
firstElement = (HASHELEMENT *) hashp->alloc(nelem * elementSize);
|
|
|
|
if (!firstElement)
|
|
return false;
|
|
|
|
/* prepare to link all the new entries into the freelist */
|
|
prevElement = NULL;
|
|
tmpElement = firstElement;
|
|
for (i = 0; i < nelem; i++)
|
|
{
|
|
tmpElement->link = prevElement;
|
|
prevElement = tmpElement;
|
|
tmpElement = (HASHELEMENT *) (((char *) tmpElement) + elementSize);
|
|
}
|
|
|
|
/* if partitioned, must lock to touch freeList */
|
|
if (IS_PARTITIONED(hctlv))
|
|
SpinLockAcquire(&hctlv->mutex);
|
|
|
|
/* freelist could be nonempty if two backends did this concurrently */
|
|
firstElement->link = hctlv->freeList;
|
|
hctlv->freeList = prevElement;
|
|
|
|
if (IS_PARTITIONED(hctlv))
|
|
SpinLockRelease(&hctlv->mutex);
|
|
|
|
return true;
|
|
}
|
|
|
|
/* complain when we have detected a corrupted hashtable */
|
|
static void
|
|
hash_corrupted(HTAB *hashp)
|
|
{
|
|
/*
|
|
* If the corruption is in a shared hashtable, we'd better force a
|
|
* systemwide restart. Otherwise, just shut down this one backend.
|
|
*/
|
|
if (hashp->isshared)
|
|
elog(PANIC, "hash table \"%s\" corrupted", hashp->tabname);
|
|
else
|
|
elog(FATAL, "hash table \"%s\" corrupted", hashp->tabname);
|
|
}
|
|
|
|
/* calculate ceil(log base 2) of num */
|
|
int
|
|
my_log2(long num)
|
|
{
|
|
int i;
|
|
long limit;
|
|
|
|
for (i = 0, limit = 1; limit < num; i++, limit <<= 1)
|
|
;
|
|
return i;
|
|
}
|
|
|
|
|
|
/************************* SEQ SCAN TRACKING ************************/
|
|
|
|
/*
|
|
* We track active hash_seq_search scans here. The need for this mechanism
|
|
* comes from the fact that a scan will get confused if a bucket split occurs
|
|
* while it's in progress: it might visit entries twice, or even miss some
|
|
* entirely (if it's partway through the same bucket that splits). Hence
|
|
* we want to inhibit bucket splits if there are any active scans on the
|
|
* table being inserted into. This is a fairly rare case in current usage,
|
|
* so just postponing the split until the next insertion seems sufficient.
|
|
*
|
|
* Given present usages of the function, only a few scans are likely to be
|
|
* open concurrently; so a finite-size stack of open scans seems sufficient,
|
|
* and we don't worry that linear search is too slow. Note that we do
|
|
* allow multiple scans of the same hashtable to be open concurrently.
|
|
*
|
|
* This mechanism can support concurrent scan and insertion in a shared
|
|
* hashtable if it's the same backend doing both. It would fail otherwise,
|
|
* but locking reasons seem to preclude any such scenario anyway, so we don't
|
|
* worry.
|
|
*
|
|
* This arrangement is reasonably robust if a transient hashtable is deleted
|
|
* without notifying us. The absolute worst case is we might inhibit splits
|
|
* in another table created later at exactly the same address. We will give
|
|
* a warning at transaction end for reference leaks, so any bugs leading to
|
|
* lack of notification should be easy to catch.
|
|
*/
|
|
|
|
#define MAX_SEQ_SCANS 100
|
|
|
|
static HTAB *seq_scan_tables[MAX_SEQ_SCANS]; /* tables being scanned */
|
|
static int seq_scan_level[MAX_SEQ_SCANS]; /* subtransaction nest level */
|
|
static int num_seq_scans = 0;
|
|
|
|
|
|
/* Register a table as having an active hash_seq_search scan */
|
|
static void
|
|
register_seq_scan(HTAB *hashp)
|
|
{
|
|
if (num_seq_scans >= MAX_SEQ_SCANS)
|
|
elog(ERROR, "too many active hash_seq_search scans, cannot start one on \"%s\"",
|
|
hashp->tabname);
|
|
seq_scan_tables[num_seq_scans] = hashp;
|
|
seq_scan_level[num_seq_scans] = GetCurrentTransactionNestLevel();
|
|
num_seq_scans++;
|
|
}
|
|
|
|
/* Deregister an active scan */
|
|
static void
|
|
deregister_seq_scan(HTAB *hashp)
|
|
{
|
|
int i;
|
|
|
|
/* Search backward since it's most likely at the stack top */
|
|
for (i = num_seq_scans - 1; i >= 0; i--)
|
|
{
|
|
if (seq_scan_tables[i] == hashp)
|
|
{
|
|
seq_scan_tables[i] = seq_scan_tables[num_seq_scans - 1];
|
|
seq_scan_level[i] = seq_scan_level[num_seq_scans - 1];
|
|
num_seq_scans--;
|
|
return;
|
|
}
|
|
}
|
|
elog(ERROR, "no hash_seq_search scan for hash table \"%s\"",
|
|
hashp->tabname);
|
|
}
|
|
|
|
/* Check if a table has any active scan */
|
|
static bool
|
|
has_seq_scans(HTAB *hashp)
|
|
{
|
|
int i;
|
|
|
|
for (i = 0; i < num_seq_scans; i++)
|
|
{
|
|
if (seq_scan_tables[i] == hashp)
|
|
return true;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
/* Clean up any open scans at end of transaction */
|
|
void
|
|
AtEOXact_HashTables(bool isCommit)
|
|
{
|
|
/*
|
|
* During abort cleanup, open scans are expected; just silently clean 'em
|
|
* out. An open scan at commit means someone forgot a hash_seq_term()
|
|
* call, so complain.
|
|
*
|
|
* Note: it's tempting to try to print the tabname here, but refrain for
|
|
* fear of touching deallocated memory. This isn't a user-facing message
|
|
* anyway, so it needn't be pretty.
|
|
*/
|
|
if (isCommit)
|
|
{
|
|
int i;
|
|
|
|
for (i = 0; i < num_seq_scans; i++)
|
|
{
|
|
elog(WARNING, "leaked hash_seq_search scan for hash table %p",
|
|
seq_scan_tables[i]);
|
|
}
|
|
}
|
|
num_seq_scans = 0;
|
|
}
|
|
|
|
/* Clean up any open scans at end of subtransaction */
|
|
void
|
|
AtEOSubXact_HashTables(bool isCommit, int nestDepth)
|
|
{
|
|
int i;
|
|
|
|
/*
|
|
* Search backward to make cleanup easy. Note we must check all entries,
|
|
* not only those at the end of the array, because deletion technique
|
|
* doesn't keep them in order.
|
|
*/
|
|
for (i = num_seq_scans - 1; i >= 0; i--)
|
|
{
|
|
if (seq_scan_level[i] >= nestDepth)
|
|
{
|
|
if (isCommit)
|
|
elog(WARNING, "leaked hash_seq_search scan for hash table %p",
|
|
seq_scan_tables[i]);
|
|
seq_scan_tables[i] = seq_scan_tables[num_seq_scans - 1];
|
|
seq_scan_level[i] = seq_scan_level[num_seq_scans - 1];
|
|
num_seq_scans--;
|
|
}
|
|
}
|
|
}
|