/*------------------------------------------------------------------------- * * nodeHash.c * Routines to hash relations for hashjoin * * Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * * * IDENTIFICATION * src/backend/executor/nodeHash.c * *------------------------------------------------------------------------- */ /* * INTERFACE ROUTINES * MultiExecHash - generate an in-memory hash table of the relation * ExecInitHash - initialize node and subnodes * ExecEndHash - shutdown node and subnodes */ #include "postgres.h" #include #include #include "catalog/pg_statistic.h" #include "commands/tablespace.h" #include "executor/execdebug.h" #include "executor/hashjoin.h" #include "executor/nodeHash.h" #include "executor/nodeHashjoin.h" #include "miscadmin.h" #include "utils/dynahash.h" #include "utils/memutils.h" #include "utils/lsyscache.h" #include "utils/syscache.h" static void ExecHashIncreaseNumBatches(HashJoinTable hashtable); static void ExecHashBuildSkewHash(HashJoinTable hashtable, Hash *node, int mcvsToUse); static void ExecHashSkewTableInsert(HashJoinTable hashtable, TupleTableSlot *slot, uint32 hashvalue, int bucketNumber); static void ExecHashRemoveNextSkewBucket(HashJoinTable hashtable); /* ---------------------------------------------------------------- * ExecHash * * stub for pro forma compliance * ---------------------------------------------------------------- */ TupleTableSlot * ExecHash(HashState *node) { elog(ERROR, "Hash node does not support ExecProcNode call convention"); return NULL; } /* ---------------------------------------------------------------- * MultiExecHash * * build hash table for hashjoin, doing partitioning if more * than one batch is required. * ---------------------------------------------------------------- */ Node * MultiExecHash(HashState *node) { PlanState *outerNode; List *hashkeys; HashJoinTable hashtable; TupleTableSlot *slot; ExprContext *econtext; uint32 hashvalue; /* must provide our own instrumentation support */ if (node->ps.instrument) InstrStartNode(node->ps.instrument); /* * get state info from node */ outerNode = outerPlanState(node); hashtable = node->hashtable; /* * set expression context */ hashkeys = node->hashkeys; econtext = node->ps.ps_ExprContext; /* * get all inner tuples and insert into the hash table (or temp files) */ for (;;) { slot = ExecProcNode(outerNode); if (TupIsNull(slot)) break; /* We have to compute the hash value */ econtext->ecxt_innertuple = slot; if (ExecHashGetHashValue(hashtable, econtext, hashkeys, false, hashtable->keepNulls, &hashvalue)) { int bucketNumber; bucketNumber = ExecHashGetSkewBucket(hashtable, hashvalue); if (bucketNumber != INVALID_SKEW_BUCKET_NO) { /* It's a skew tuple, so put it into that hash table */ ExecHashSkewTableInsert(hashtable, slot, hashvalue, bucketNumber); } else { /* Not subject to skew optimization, so insert normally */ ExecHashTableInsert(hashtable, slot, hashvalue); } hashtable->totalTuples += 1; } } /* must provide our own instrumentation support */ if (node->ps.instrument) InstrStopNode(node->ps.instrument, hashtable->totalTuples); /* * We do not return the hash table directly because it's not a subtype of * Node, and so would violate the MultiExecProcNode API. Instead, our * parent Hashjoin node is expected to know how to fish it out of our node * state. Ugly but not really worth cleaning up, since Hashjoin knows * quite a bit more about Hash besides that. */ return NULL; } /* ---------------------------------------------------------------- * ExecInitHash * * Init routine for Hash node * ---------------------------------------------------------------- */ HashState * ExecInitHash(Hash *node, EState *estate, int eflags) { HashState *hashstate; /* check for unsupported flags */ Assert(!(eflags & (EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK))); /* * create state structure */ hashstate = makeNode(HashState); hashstate->ps.plan = (Plan *) node; hashstate->ps.state = estate; hashstate->hashtable = NULL; hashstate->hashkeys = NIL; /* will be set by parent HashJoin */ /* * Miscellaneous initialization * * create expression context for node */ ExecAssignExprContext(estate, &hashstate->ps); /* * initialize our result slot */ ExecInitResultTupleSlot(estate, &hashstate->ps); /* * initialize child expressions */ hashstate->ps.targetlist = (List *) ExecInitExpr((Expr *) node->plan.targetlist, (PlanState *) hashstate); hashstate->ps.qual = (List *) ExecInitExpr((Expr *) node->plan.qual, (PlanState *) hashstate); /* * initialize child nodes */ outerPlanState(hashstate) = ExecInitNode(outerPlan(node), estate, eflags); /* * initialize tuple type. no need to initialize projection info because * this node doesn't do projections */ ExecAssignResultTypeFromTL(&hashstate->ps); hashstate->ps.ps_ProjInfo = NULL; return hashstate; } /* --------------------------------------------------------------- * ExecEndHash * * clean up routine for Hash node * ---------------------------------------------------------------- */ void ExecEndHash(HashState *node) { PlanState *outerPlan; /* * free exprcontext */ ExecFreeExprContext(&node->ps); /* * shut down the subplan */ outerPlan = outerPlanState(node); ExecEndNode(outerPlan); } /* ---------------------------------------------------------------- * ExecHashTableCreate * * create an empty hashtable data structure for hashjoin. * ---------------------------------------------------------------- */ HashJoinTable ExecHashTableCreate(Hash *node, List *hashOperators, bool keepNulls) { HashJoinTable hashtable; Plan *outerNode; int nbuckets; int nbatch; int num_skew_mcvs; int log2_nbuckets; int nkeys; int i; ListCell *ho; MemoryContext oldcxt; /* * Get information about the size of the relation to be hashed (it's the * "outer" subtree of this node, but the inner relation of the hashjoin). * Compute the appropriate size of the hash table. */ outerNode = outerPlan(node); ExecChooseHashTableSize(outerNode->plan_rows, outerNode->plan_width, OidIsValid(node->skewTable), &nbuckets, &nbatch, &num_skew_mcvs); #ifdef HJDEBUG printf("nbatch = %d, nbuckets = %d\n", nbatch, nbuckets); #endif /* nbuckets must be a power of 2 */ log2_nbuckets = my_log2(nbuckets); Assert(nbuckets == (1 << log2_nbuckets)); /* * Initialize the hash table control block. * * The hashtable control block is just palloc'd from the executor's * per-query memory context. */ hashtable = (HashJoinTable) palloc(sizeof(HashJoinTableData)); hashtable->nbuckets = nbuckets; hashtable->log2_nbuckets = log2_nbuckets; hashtable->buckets = NULL; hashtable->keepNulls = keepNulls; hashtable->skewEnabled = false; hashtable->skewBucket = NULL; hashtable->skewBucketLen = 0; hashtable->nSkewBuckets = 0; hashtable->skewBucketNums = NULL; hashtable->nbatch = nbatch; hashtable->curbatch = 0; hashtable->nbatch_original = nbatch; hashtable->nbatch_outstart = nbatch; hashtable->growEnabled = true; hashtable->totalTuples = 0; hashtable->innerBatchFile = NULL; hashtable->outerBatchFile = NULL; hashtable->spaceUsed = 0; hashtable->spacePeak = 0; hashtable->spaceAllowed = work_mem * 1024L; hashtable->spaceUsedSkew = 0; hashtable->spaceAllowedSkew = hashtable->spaceAllowed * SKEW_WORK_MEM_PERCENT / 100; /* * Get info about the hash functions to be used for each hash key. Also * remember whether the join operators are strict. */ nkeys = list_length(hashOperators); hashtable->outer_hashfunctions = (FmgrInfo *) palloc(nkeys * sizeof(FmgrInfo)); hashtable->inner_hashfunctions = (FmgrInfo *) palloc(nkeys * sizeof(FmgrInfo)); hashtable->hashStrict = (bool *) palloc(nkeys * sizeof(bool)); i = 0; foreach(ho, hashOperators) { Oid hashop = lfirst_oid(ho); Oid left_hashfn; Oid right_hashfn; if (!get_op_hash_functions(hashop, &left_hashfn, &right_hashfn)) elog(ERROR, "could not find hash function for hash operator %u", hashop); fmgr_info(left_hashfn, &hashtable->outer_hashfunctions[i]); fmgr_info(right_hashfn, &hashtable->inner_hashfunctions[i]); hashtable->hashStrict[i] = op_strict(hashop); i++; } /* * Create temporary memory contexts in which to keep the hashtable working * storage. See notes in executor/hashjoin.h. */ hashtable->hashCxt = AllocSetContextCreate(CurrentMemoryContext, "HashTableContext", ALLOCSET_DEFAULT_MINSIZE, ALLOCSET_DEFAULT_INITSIZE, ALLOCSET_DEFAULT_MAXSIZE); hashtable->batchCxt = AllocSetContextCreate(hashtable->hashCxt, "HashBatchContext", ALLOCSET_DEFAULT_MINSIZE, ALLOCSET_DEFAULT_INITSIZE, ALLOCSET_DEFAULT_MAXSIZE); /* Allocate data that will live for the life of the hashjoin */ oldcxt = MemoryContextSwitchTo(hashtable->hashCxt); if (nbatch > 1) { /* * allocate and initialize the file arrays in hashCxt */ hashtable->innerBatchFile = (BufFile **) palloc0(nbatch * sizeof(BufFile *)); hashtable->outerBatchFile = (BufFile **) palloc0(nbatch * sizeof(BufFile *)); /* The files will not be opened until needed... */ /* ... but make sure we have temp tablespaces established for them */ PrepareTempTablespaces(); } /* * Prepare context for the first-scan space allocations; allocate the * hashbucket array therein, and set each bucket "empty". */ MemoryContextSwitchTo(hashtable->batchCxt); hashtable->buckets = (HashJoinTuple *) palloc0(nbuckets * sizeof(HashJoinTuple)); /* * Set up for skew optimization, if possible and there's a need for more * than one batch. (In a one-batch join, there's no point in it.) */ if (nbatch > 1) ExecHashBuildSkewHash(hashtable, node, num_skew_mcvs); MemoryContextSwitchTo(oldcxt); return hashtable; } /* * Compute appropriate size for hashtable given the estimated size of the * relation to be hashed (number of rows and average row width). * * This is exported so that the planner's costsize.c can use it. */ /* Target bucket loading (tuples per bucket) */ #define NTUP_PER_BUCKET 10 void ExecChooseHashTableSize(double ntuples, int tupwidth, bool useskew, int *numbuckets, int *numbatches, int *num_skew_mcvs) { int tupsize; double inner_rel_bytes; long hash_table_bytes; long skew_table_bytes; long max_pointers; int nbatch; int nbuckets; int i; /* Force a plausible relation size if no info */ if (ntuples <= 0.0) ntuples = 1000.0; /* * Estimate tupsize based on footprint of tuple in hashtable... note this * does not allow for any palloc overhead. The manipulations of spaceUsed * don't count palloc overhead either. */ tupsize = HJTUPLE_OVERHEAD + MAXALIGN(sizeof(MinimalTupleData)) + MAXALIGN(tupwidth); inner_rel_bytes = ntuples * tupsize; /* * Target in-memory hashtable size is work_mem kilobytes. */ hash_table_bytes = work_mem * 1024L; /* * If skew optimization is possible, estimate the number of skew buckets * that will fit in the memory allowed, and decrement the assumed space * available for the main hash table accordingly. * * We make the optimistic assumption that each skew bucket will contain * one inner-relation tuple. If that turns out to be low, we will recover * at runtime by reducing the number of skew buckets. * * hashtable->skewBucket will have up to 8 times as many HashSkewBucket * pointers as the number of MCVs we allow, since ExecHashBuildSkewHash * will round up to the next power of 2 and then multiply by 4 to reduce * collisions. */ if (useskew) { skew_table_bytes = hash_table_bytes * SKEW_WORK_MEM_PERCENT / 100; /*---------- * Divisor is: * size of a hash tuple + * worst-case size of skewBucket[] per MCV + * size of skewBucketNums[] entry + * size of skew bucket struct itself *---------- */ *num_skew_mcvs = skew_table_bytes / (tupsize + (8 * sizeof(HashSkewBucket *)) + sizeof(int) + SKEW_BUCKET_OVERHEAD); if (*num_skew_mcvs > 0) hash_table_bytes -= skew_table_bytes; } else *num_skew_mcvs = 0; /* * Set nbuckets to achieve an average bucket load of NTUP_PER_BUCKET when * memory is filled. Set nbatch to the smallest power of 2 that appears * sufficient. The Min() steps limit the results so that the pointer * arrays we'll try to allocate do not exceed work_mem. */ max_pointers = (work_mem * 1024L) / sizeof(void *); /* also ensure we avoid integer overflow in nbatch and nbuckets */ max_pointers = Min(max_pointers, INT_MAX / 2); if (inner_rel_bytes > hash_table_bytes) { /* We'll need multiple batches */ long lbuckets; double dbatch; int minbatch; lbuckets = (hash_table_bytes / tupsize) / NTUP_PER_BUCKET; lbuckets = Min(lbuckets, max_pointers); nbuckets = (int) lbuckets; dbatch = ceil(inner_rel_bytes / hash_table_bytes); dbatch = Min(dbatch, max_pointers); minbatch = (int) dbatch; nbatch = 2; while (nbatch < minbatch) nbatch <<= 1; } else { /* We expect the hashtable to fit in memory */ double dbuckets; dbuckets = ceil(ntuples / NTUP_PER_BUCKET); dbuckets = Min(dbuckets, max_pointers); nbuckets = (int) dbuckets; nbatch = 1; } /* * Both nbuckets and nbatch must be powers of 2 to make * ExecHashGetBucketAndBatch fast. We already fixed nbatch; now inflate * nbuckets to the next larger power of 2. We also force nbuckets to not * be real small, by starting the search at 2^10. */ i = 10; while ((1 << i) < nbuckets) i++; nbuckets = (1 << i); *numbuckets = nbuckets; *numbatches = nbatch; } /* ---------------------------------------------------------------- * ExecHashTableDestroy * * destroy a hash table * ---------------------------------------------------------------- */ void ExecHashTableDestroy(HashJoinTable hashtable) { int i; /* * Make sure all the temp files are closed. We skip batch 0, since it * can't have any temp files (and the arrays might not even exist if * nbatch is only 1). */ for (i = 1; i < hashtable->nbatch; i++) { if (hashtable->innerBatchFile[i]) BufFileClose(hashtable->innerBatchFile[i]); if (hashtable->outerBatchFile[i]) BufFileClose(hashtable->outerBatchFile[i]); } /* Release working memory (batchCxt is a child, so it goes away too) */ MemoryContextDelete(hashtable->hashCxt); /* And drop the control block */ pfree(hashtable); } /* * ExecHashIncreaseNumBatches * increase the original number of batches in order to reduce * current memory consumption */ static void ExecHashIncreaseNumBatches(HashJoinTable hashtable) { int oldnbatch = hashtable->nbatch; int curbatch = hashtable->curbatch; int nbatch; int i; MemoryContext oldcxt; long ninmemory; long nfreed; /* do nothing if we've decided to shut off growth */ if (!hashtable->growEnabled) return; /* safety check to avoid overflow */ if (oldnbatch > Min(INT_MAX / 2, MaxAllocSize / (sizeof(void *) * 2))) return; nbatch = oldnbatch * 2; Assert(nbatch > 1); #ifdef HJDEBUG printf("Increasing nbatch to %d because space = %lu\n", nbatch, (unsigned long) hashtable->spaceUsed); #endif oldcxt = MemoryContextSwitchTo(hashtable->hashCxt); if (hashtable->innerBatchFile == NULL) { /* we had no file arrays before */ hashtable->innerBatchFile = (BufFile **) palloc0(nbatch * sizeof(BufFile *)); hashtable->outerBatchFile = (BufFile **) palloc0(nbatch * sizeof(BufFile *)); /* time to establish the temp tablespaces, too */ PrepareTempTablespaces(); } else { /* enlarge arrays and zero out added entries */ hashtable->innerBatchFile = (BufFile **) repalloc(hashtable->innerBatchFile, nbatch * sizeof(BufFile *)); hashtable->outerBatchFile = (BufFile **) repalloc(hashtable->outerBatchFile, nbatch * sizeof(BufFile *)); MemSet(hashtable->innerBatchFile + oldnbatch, 0, (nbatch - oldnbatch) * sizeof(BufFile *)); MemSet(hashtable->outerBatchFile + oldnbatch, 0, (nbatch - oldnbatch) * sizeof(BufFile *)); } MemoryContextSwitchTo(oldcxt); hashtable->nbatch = nbatch; /* * Scan through the existing hash table entries and dump out any that are * no longer of the current batch. */ ninmemory = nfreed = 0; for (i = 0; i < hashtable->nbuckets; i++) { HashJoinTuple prevtuple; HashJoinTuple tuple; prevtuple = NULL; tuple = hashtable->buckets[i]; while (tuple != NULL) { /* save link in case we delete */ HashJoinTuple nexttuple = tuple->next; int bucketno; int batchno; ninmemory++; ExecHashGetBucketAndBatch(hashtable, tuple->hashvalue, &bucketno, &batchno); Assert(bucketno == i); if (batchno == curbatch) { /* keep tuple */ prevtuple = tuple; } else { /* dump it out */ Assert(batchno > curbatch); ExecHashJoinSaveTuple(HJTUPLE_MINTUPLE(tuple), tuple->hashvalue, &hashtable->innerBatchFile[batchno]); /* and remove from hash table */ if (prevtuple) prevtuple->next = nexttuple; else hashtable->buckets[i] = nexttuple; /* prevtuple doesn't change */ hashtable->spaceUsed -= HJTUPLE_OVERHEAD + HJTUPLE_MINTUPLE(tuple)->t_len; pfree(tuple); nfreed++; } tuple = nexttuple; } } #ifdef HJDEBUG printf("Freed %ld of %ld tuples, space now %lu\n", nfreed, ninmemory, (unsigned long) hashtable->spaceUsed); #endif /* * If we dumped out either all or none of the tuples in the table, disable * further expansion of nbatch. This situation implies that we have * enough tuples of identical hashvalues to overflow spaceAllowed. * Increasing nbatch will not fix it since there's no way to subdivide the * group any more finely. We have to just gut it out and hope the server * has enough RAM. */ if (nfreed == 0 || nfreed == ninmemory) { hashtable->growEnabled = false; #ifdef HJDEBUG printf("Disabling further increase of nbatch\n"); #endif } } /* * ExecHashTableInsert * insert a tuple into the hash table depending on the hash value * it may just go to a temp file for later batches * * Note: the passed TupleTableSlot may contain a regular, minimal, or virtual * tuple; the minimal case in particular is certain to happen while reloading * tuples from batch files. We could save some cycles in the regular-tuple * case by not forcing the slot contents into minimal form; not clear if it's * worth the messiness required. */ void ExecHashTableInsert(HashJoinTable hashtable, TupleTableSlot *slot, uint32 hashvalue) { MinimalTuple tuple = ExecFetchSlotMinimalTuple(slot); int bucketno; int batchno; ExecHashGetBucketAndBatch(hashtable, hashvalue, &bucketno, &batchno); /* * decide whether to put the tuple in the hash table or a temp file */ if (batchno == hashtable->curbatch) { /* * put the tuple in hash table */ HashJoinTuple hashTuple; int hashTupleSize; /* Create the HashJoinTuple */ hashTupleSize = HJTUPLE_OVERHEAD + tuple->t_len; hashTuple = (HashJoinTuple) MemoryContextAlloc(hashtable->batchCxt, hashTupleSize); hashTuple->hashvalue = hashvalue; memcpy(HJTUPLE_MINTUPLE(hashTuple), tuple, tuple->t_len); /* * We always reset the tuple-matched flag on insertion. This is okay * even when reloading a tuple from a batch file, since the tuple * could not possibly have been matched to an outer tuple before it * went into the batch file. */ HeapTupleHeaderClearMatch(HJTUPLE_MINTUPLE(hashTuple)); /* Push it onto the front of the bucket's list */ hashTuple->next = hashtable->buckets[bucketno]; hashtable->buckets[bucketno] = hashTuple; /* Account for space used, and back off if we've used too much */ hashtable->spaceUsed += hashTupleSize; if (hashtable->spaceUsed > hashtable->spacePeak) hashtable->spacePeak = hashtable->spaceUsed; if (hashtable->spaceUsed > hashtable->spaceAllowed) ExecHashIncreaseNumBatches(hashtable); } else { /* * put the tuple into a temp file for later batches */ Assert(batchno > hashtable->curbatch); ExecHashJoinSaveTuple(tuple, hashvalue, &hashtable->innerBatchFile[batchno]); } } /* * ExecHashGetHashValue * Compute the hash value for a tuple * * The tuple to be tested must be in either econtext->ecxt_outertuple or * econtext->ecxt_innertuple. Vars in the hashkeys expressions should have * varno either OUTER_VAR or INNER_VAR. * * A TRUE result means the tuple's hash value has been successfully computed * and stored at *hashvalue. A FALSE result means the tuple cannot match * because it contains a null attribute, and hence it should be discarded * immediately. (If keep_nulls is true then FALSE is never returned.) */ bool ExecHashGetHashValue(HashJoinTable hashtable, ExprContext *econtext, List *hashkeys, bool outer_tuple, bool keep_nulls, uint32 *hashvalue) { uint32 hashkey = 0; FmgrInfo *hashfunctions; ListCell *hk; int i = 0; MemoryContext oldContext; /* * We reset the eval context each time to reclaim any memory leaked in the * hashkey expressions. */ ResetExprContext(econtext); oldContext = MemoryContextSwitchTo(econtext->ecxt_per_tuple_memory); if (outer_tuple) hashfunctions = hashtable->outer_hashfunctions; else hashfunctions = hashtable->inner_hashfunctions; foreach(hk, hashkeys) { ExprState *keyexpr = (ExprState *) lfirst(hk); Datum keyval; bool isNull; /* rotate hashkey left 1 bit at each step */ hashkey = (hashkey << 1) | ((hashkey & 0x80000000) ? 1 : 0); /* * Get the join attribute value of the tuple */ keyval = ExecEvalExpr(keyexpr, econtext, &isNull, NULL); /* * If the attribute is NULL, and the join operator is strict, then * this tuple cannot pass the join qual so we can reject it * immediately (unless we're scanning the outside of an outer join, in * which case we must not reject it). Otherwise we act like the * hashcode of NULL is zero (this will support operators that act like * IS NOT DISTINCT, though not any more-random behavior). We treat * the hash support function as strict even if the operator is not. * * Note: currently, all hashjoinable operators must be strict since * the hash index AM assumes that. However, it takes so little extra * code here to allow non-strict that we may as well do it. */ if (isNull) { if (hashtable->hashStrict[i] && !keep_nulls) { MemoryContextSwitchTo(oldContext); return false; /* cannot match */ } /* else, leave hashkey unmodified, equivalent to hashcode 0 */ } else { /* Compute the hash function */ uint32 hkey; hkey = DatumGetUInt32(FunctionCall1(&hashfunctions[i], keyval)); hashkey ^= hkey; } i++; } MemoryContextSwitchTo(oldContext); *hashvalue = hashkey; return true; } /* * ExecHashGetBucketAndBatch * Determine the bucket number and batch number for a hash value * * Note: on-the-fly increases of nbatch must not change the bucket number * for a given hash code (since we don't move tuples to different hash * chains), and must only cause the batch number to remain the same or * increase. Our algorithm is * bucketno = hashvalue MOD nbuckets * batchno = (hashvalue DIV nbuckets) MOD nbatch * where nbuckets and nbatch are both expected to be powers of 2, so we can * do the computations by shifting and masking. (This assumes that all hash * functions are good about randomizing all their output bits, else we are * likely to have very skewed bucket or batch occupancy.) * * nbuckets doesn't change over the course of the join. * * nbatch is always a power of 2; we increase it only by doubling it. This * effectively adds one more bit to the top of the batchno. */ void ExecHashGetBucketAndBatch(HashJoinTable hashtable, uint32 hashvalue, int *bucketno, int *batchno) { uint32 nbuckets = (uint32) hashtable->nbuckets; uint32 nbatch = (uint32) hashtable->nbatch; if (nbatch > 1) { /* we can do MOD by masking, DIV by shifting */ *bucketno = hashvalue & (nbuckets - 1); *batchno = (hashvalue >> hashtable->log2_nbuckets) & (nbatch - 1); } else { *bucketno = hashvalue & (nbuckets - 1); *batchno = 0; } } /* * ExecScanHashBucket * scan a hash bucket for matches to the current outer tuple * * The current outer tuple must be stored in econtext->ecxt_outertuple. * * On success, the inner tuple is stored into hjstate->hj_CurTuple and * econtext->ecxt_innertuple, using hjstate->hj_HashTupleSlot as the slot * for the latter. */ bool ExecScanHashBucket(HashJoinState *hjstate, ExprContext *econtext) { List *hjclauses = hjstate->hashclauses; HashJoinTable hashtable = hjstate->hj_HashTable; HashJoinTuple hashTuple = hjstate->hj_CurTuple; uint32 hashvalue = hjstate->hj_CurHashValue; /* * hj_CurTuple is the address of the tuple last returned from the current * bucket, or NULL if it's time to start scanning a new bucket. * * If the tuple hashed to a skew bucket then scan the skew bucket * otherwise scan the standard hashtable bucket. */ if (hashTuple != NULL) hashTuple = hashTuple->next; else if (hjstate->hj_CurSkewBucketNo != INVALID_SKEW_BUCKET_NO) hashTuple = hashtable->skewBucket[hjstate->hj_CurSkewBucketNo]->tuples; else hashTuple = hashtable->buckets[hjstate->hj_CurBucketNo]; while (hashTuple != NULL) { if (hashTuple->hashvalue == hashvalue) { TupleTableSlot *inntuple; /* insert hashtable's tuple into exec slot so ExecQual sees it */ inntuple = ExecStoreMinimalTuple(HJTUPLE_MINTUPLE(hashTuple), hjstate->hj_HashTupleSlot, false); /* do not pfree */ econtext->ecxt_innertuple = inntuple; /* reset temp memory each time to avoid leaks from qual expr */ ResetExprContext(econtext); if (ExecQual(hjclauses, econtext, false)) { hjstate->hj_CurTuple = hashTuple; return true; } } hashTuple = hashTuple->next; } /* * no match */ return false; } /* * ExecPrepHashTableForUnmatched * set up for a series of ExecScanHashTableForUnmatched calls */ void ExecPrepHashTableForUnmatched(HashJoinState *hjstate) { /* * ---------- During this scan we use the HashJoinState fields as follows: * * hj_CurBucketNo: next regular bucket to scan hj_CurSkewBucketNo: next * skew bucket (an index into skewBucketNums) hj_CurTuple: last tuple * returned, or NULL to start next bucket ---------- */ hjstate->hj_CurBucketNo = 0; hjstate->hj_CurSkewBucketNo = 0; hjstate->hj_CurTuple = NULL; } /* * ExecScanHashTableForUnmatched * scan the hash table for unmatched inner tuples * * On success, the inner tuple is stored into hjstate->hj_CurTuple and * econtext->ecxt_innertuple, using hjstate->hj_HashTupleSlot as the slot * for the latter. */ bool ExecScanHashTableForUnmatched(HashJoinState *hjstate, ExprContext *econtext) { HashJoinTable hashtable = hjstate->hj_HashTable; HashJoinTuple hashTuple = hjstate->hj_CurTuple; for (;;) { /* * hj_CurTuple is the address of the tuple last returned from the * current bucket, or NULL if it's time to start scanning a new * bucket. */ if (hashTuple != NULL) hashTuple = hashTuple->next; else if (hjstate->hj_CurBucketNo < hashtable->nbuckets) { hashTuple = hashtable->buckets[hjstate->hj_CurBucketNo]; hjstate->hj_CurBucketNo++; } else if (hjstate->hj_CurSkewBucketNo < hashtable->nSkewBuckets) { int j = hashtable->skewBucketNums[hjstate->hj_CurSkewBucketNo]; hashTuple = hashtable->skewBucket[j]->tuples; hjstate->hj_CurSkewBucketNo++; } else break; /* finished all buckets */ while (hashTuple != NULL) { if (!HeapTupleHeaderHasMatch(HJTUPLE_MINTUPLE(hashTuple))) { TupleTableSlot *inntuple; /* insert hashtable's tuple into exec slot */ inntuple = ExecStoreMinimalTuple(HJTUPLE_MINTUPLE(hashTuple), hjstate->hj_HashTupleSlot, false); /* do not pfree */ econtext->ecxt_innertuple = inntuple; /* * Reset temp memory each time; although this function doesn't * do any qual eval, the caller will, so let's keep it * parallel to ExecScanHashBucket. */ ResetExprContext(econtext); hjstate->hj_CurTuple = hashTuple; return true; } hashTuple = hashTuple->next; } } /* * no more unmatched tuples */ return false; } /* * ExecHashTableReset * * reset hash table header for new batch */ void ExecHashTableReset(HashJoinTable hashtable) { MemoryContext oldcxt; int nbuckets = hashtable->nbuckets; /* * Release all the hash buckets and tuples acquired in the prior pass, and * reinitialize the context for a new pass. */ MemoryContextReset(hashtable->batchCxt); oldcxt = MemoryContextSwitchTo(hashtable->batchCxt); /* Reallocate and reinitialize the hash bucket headers. */ hashtable->buckets = (HashJoinTuple *) palloc0(nbuckets * sizeof(HashJoinTuple)); hashtable->spaceUsed = 0; MemoryContextSwitchTo(oldcxt); } /* * ExecHashTableResetMatchFlags * Clear all the HeapTupleHeaderHasMatch flags in the table */ void ExecHashTableResetMatchFlags(HashJoinTable hashtable) { HashJoinTuple tuple; int i; /* Reset all flags in the main table ... */ for (i = 0; i < hashtable->nbuckets; i++) { for (tuple = hashtable->buckets[i]; tuple != NULL; tuple = tuple->next) HeapTupleHeaderClearMatch(HJTUPLE_MINTUPLE(tuple)); } /* ... and the same for the skew buckets, if any */ for (i = 0; i < hashtable->nSkewBuckets; i++) { int j = hashtable->skewBucketNums[i]; HashSkewBucket *skewBucket = hashtable->skewBucket[j]; for (tuple = skewBucket->tuples; tuple != NULL; tuple = tuple->next) HeapTupleHeaderClearMatch(HJTUPLE_MINTUPLE(tuple)); } } void ExecReScanHash(HashState *node) { /* * if chgParam of subnode is not null then plan will be re-scanned by * first ExecProcNode. */ if (node->ps.lefttree->chgParam == NULL) ExecReScan(node->ps.lefttree); } /* * ExecHashBuildSkewHash * * Set up for skew optimization if we can identify the most common values * (MCVs) of the outer relation's join key. We make a skew hash bucket * for the hash value of each MCV, up to the number of slots allowed * based on available memory. */ static void ExecHashBuildSkewHash(HashJoinTable hashtable, Hash *node, int mcvsToUse) { HeapTupleData *statsTuple; Datum *values; int nvalues; float4 *numbers; int nnumbers; /* Do nothing if planner didn't identify the outer relation's join key */ if (!OidIsValid(node->skewTable)) return; /* Also, do nothing if we don't have room for at least one skew bucket */ if (mcvsToUse <= 0) return; /* * Try to find the MCV statistics for the outer relation's join key. */ statsTuple = SearchSysCache3(STATRELATTINH, ObjectIdGetDatum(node->skewTable), Int16GetDatum(node->skewColumn), BoolGetDatum(node->skewInherit)); if (!HeapTupleIsValid(statsTuple)) return; if (get_attstatsslot(statsTuple, node->skewColType, node->skewColTypmod, STATISTIC_KIND_MCV, InvalidOid, NULL, &values, &nvalues, &numbers, &nnumbers)) { double frac; int nbuckets; FmgrInfo *hashfunctions; int i; if (mcvsToUse > nvalues) mcvsToUse = nvalues; /* * Calculate the expected fraction of outer relation that will * participate in the skew optimization. If this isn't at least * SKEW_MIN_OUTER_FRACTION, don't use skew optimization. */ frac = 0; for (i = 0; i < mcvsToUse; i++) frac += numbers[i]; if (frac < SKEW_MIN_OUTER_FRACTION) { free_attstatsslot(node->skewColType, values, nvalues, numbers, nnumbers); ReleaseSysCache(statsTuple); return; } /* * Okay, set up the skew hashtable. * * skewBucket[] is an open addressing hashtable with a power of 2 size * that is greater than the number of MCV values. (This ensures there * will be at least one null entry, so searches will always * terminate.) * * Note: this code could fail if mcvsToUse exceeds INT_MAX/8 or * MaxAllocSize/sizeof(void *)/8, but that is not currently possible * since we limit pg_statistic entries to much less than that. */ nbuckets = 2; while (nbuckets <= mcvsToUse) nbuckets <<= 1; /* use two more bits just to help avoid collisions */ nbuckets <<= 2; hashtable->skewEnabled = true; hashtable->skewBucketLen = nbuckets; /* * We allocate the bucket memory in the hashtable's batch context. It * is only needed during the first batch, and this ensures it will be * automatically removed once the first batch is done. */ hashtable->skewBucket = (HashSkewBucket **) MemoryContextAllocZero(hashtable->batchCxt, nbuckets * sizeof(HashSkewBucket *)); hashtable->skewBucketNums = (int *) MemoryContextAllocZero(hashtable->batchCxt, mcvsToUse * sizeof(int)); hashtable->spaceUsed += nbuckets * sizeof(HashSkewBucket *) + mcvsToUse * sizeof(int); hashtable->spaceUsedSkew += nbuckets * sizeof(HashSkewBucket *) + mcvsToUse * sizeof(int); if (hashtable->spaceUsed > hashtable->spacePeak) hashtable->spacePeak = hashtable->spaceUsed; /* * Create a skew bucket for each MCV hash value. * * Note: it is very important that we create the buckets in order of * decreasing MCV frequency. If we have to remove some buckets, they * must be removed in reverse order of creation (see notes in * ExecHashRemoveNextSkewBucket) and we want the least common MCVs to * be removed first. */ hashfunctions = hashtable->outer_hashfunctions; for (i = 0; i < mcvsToUse; i++) { uint32 hashvalue; int bucket; hashvalue = DatumGetUInt32(FunctionCall1(&hashfunctions[0], values[i])); /* * While we have not hit a hole in the hashtable and have not hit * the desired bucket, we have collided with some previous hash * value, so try the next bucket location. NB: this code must * match ExecHashGetSkewBucket. */ bucket = hashvalue & (nbuckets - 1); while (hashtable->skewBucket[bucket] != NULL && hashtable->skewBucket[bucket]->hashvalue != hashvalue) bucket = (bucket + 1) & (nbuckets - 1); /* * If we found an existing bucket with the same hashvalue, leave * it alone. It's okay for two MCVs to share a hashvalue. */ if (hashtable->skewBucket[bucket] != NULL) continue; /* Okay, create a new skew bucket for this hashvalue. */ hashtable->skewBucket[bucket] = (HashSkewBucket *) MemoryContextAlloc(hashtable->batchCxt, sizeof(HashSkewBucket)); hashtable->skewBucket[bucket]->hashvalue = hashvalue; hashtable->skewBucket[bucket]->tuples = NULL; hashtable->skewBucketNums[hashtable->nSkewBuckets] = bucket; hashtable->nSkewBuckets++; hashtable->spaceUsed += SKEW_BUCKET_OVERHEAD; hashtable->spaceUsedSkew += SKEW_BUCKET_OVERHEAD; if (hashtable->spaceUsed > hashtable->spacePeak) hashtable->spacePeak = hashtable->spaceUsed; } free_attstatsslot(node->skewColType, values, nvalues, numbers, nnumbers); } ReleaseSysCache(statsTuple); } /* * ExecHashGetSkewBucket * * Returns the index of the skew bucket for this hashvalue, * or INVALID_SKEW_BUCKET_NO if the hashvalue is not * associated with any active skew bucket. */ int ExecHashGetSkewBucket(HashJoinTable hashtable, uint32 hashvalue) { int bucket; /* * Always return INVALID_SKEW_BUCKET_NO if not doing skew optimization (in * particular, this happens after the initial batch is done). */ if (!hashtable->skewEnabled) return INVALID_SKEW_BUCKET_NO; /* * Since skewBucketLen is a power of 2, we can do a modulo by ANDing. */ bucket = hashvalue & (hashtable->skewBucketLen - 1); /* * While we have not hit a hole in the hashtable and have not hit the * desired bucket, we have collided with some other hash value, so try the * next bucket location. */ while (hashtable->skewBucket[bucket] != NULL && hashtable->skewBucket[bucket]->hashvalue != hashvalue) bucket = (bucket + 1) & (hashtable->skewBucketLen - 1); /* * Found the desired bucket? */ if (hashtable->skewBucket[bucket] != NULL) return bucket; /* * There must not be any hashtable entry for this hash value. */ return INVALID_SKEW_BUCKET_NO; } /* * ExecHashSkewTableInsert * * Insert a tuple into the skew hashtable. * * This should generally match up with the current-batch case in * ExecHashTableInsert. */ static void ExecHashSkewTableInsert(HashJoinTable hashtable, TupleTableSlot *slot, uint32 hashvalue, int bucketNumber) { MinimalTuple tuple = ExecFetchSlotMinimalTuple(slot); HashJoinTuple hashTuple; int hashTupleSize; /* Create the HashJoinTuple */ hashTupleSize = HJTUPLE_OVERHEAD + tuple->t_len; hashTuple = (HashJoinTuple) MemoryContextAlloc(hashtable->batchCxt, hashTupleSize); hashTuple->hashvalue = hashvalue; memcpy(HJTUPLE_MINTUPLE(hashTuple), tuple, tuple->t_len); HeapTupleHeaderClearMatch(HJTUPLE_MINTUPLE(hashTuple)); /* Push it onto the front of the skew bucket's list */ hashTuple->next = hashtable->skewBucket[bucketNumber]->tuples; hashtable->skewBucket[bucketNumber]->tuples = hashTuple; /* Account for space used, and back off if we've used too much */ hashtable->spaceUsed += hashTupleSize; hashtable->spaceUsedSkew += hashTupleSize; if (hashtable->spaceUsed > hashtable->spacePeak) hashtable->spacePeak = hashtable->spaceUsed; while (hashtable->spaceUsedSkew > hashtable->spaceAllowedSkew) ExecHashRemoveNextSkewBucket(hashtable); /* Check we are not over the total spaceAllowed, either */ if (hashtable->spaceUsed > hashtable->spaceAllowed) ExecHashIncreaseNumBatches(hashtable); } /* * ExecHashRemoveNextSkewBucket * * Remove the least valuable skew bucket by pushing its tuples into * the main hash table. */ static void ExecHashRemoveNextSkewBucket(HashJoinTable hashtable) { int bucketToRemove; HashSkewBucket *bucket; uint32 hashvalue; int bucketno; int batchno; HashJoinTuple hashTuple; /* Locate the bucket to remove */ bucketToRemove = hashtable->skewBucketNums[hashtable->nSkewBuckets - 1]; bucket = hashtable->skewBucket[bucketToRemove]; /* * Calculate which bucket and batch the tuples belong to in the main * hashtable. They all have the same hash value, so it's the same for all * of them. Also note that it's not possible for nbatch to increase while * we are processing the tuples. */ hashvalue = bucket->hashvalue; ExecHashGetBucketAndBatch(hashtable, hashvalue, &bucketno, &batchno); /* Process all tuples in the bucket */ hashTuple = bucket->tuples; while (hashTuple != NULL) { HashJoinTuple nextHashTuple = hashTuple->next; MinimalTuple tuple; Size tupleSize; /* * This code must agree with ExecHashTableInsert. We do not use * ExecHashTableInsert directly as ExecHashTableInsert expects a * TupleTableSlot while we already have HashJoinTuples. */ tuple = HJTUPLE_MINTUPLE(hashTuple); tupleSize = HJTUPLE_OVERHEAD + tuple->t_len; /* Decide whether to put the tuple in the hash table or a temp file */ if (batchno == hashtable->curbatch) { /* Move the tuple to the main hash table */ hashTuple->next = hashtable->buckets[bucketno]; hashtable->buckets[bucketno] = hashTuple; /* We have reduced skew space, but overall space doesn't change */ hashtable->spaceUsedSkew -= tupleSize; } else { /* Put the tuple into a temp file for later batches */ Assert(batchno > hashtable->curbatch); ExecHashJoinSaveTuple(tuple, hashvalue, &hashtable->innerBatchFile[batchno]); pfree(hashTuple); hashtable->spaceUsed -= tupleSize; hashtable->spaceUsedSkew -= tupleSize; } hashTuple = nextHashTuple; } /* * Free the bucket struct itself and reset the hashtable entry to NULL. * * NOTE: this is not nearly as simple as it looks on the surface, because * of the possibility of collisions in the hashtable. Suppose that hash * values A and B collide at a particular hashtable entry, and that A was * entered first so B gets shifted to a different table entry. If we were * to remove A first then ExecHashGetSkewBucket would mistakenly start * reporting that B is not in the hashtable, because it would hit the NULL * before finding B. However, we always remove entries in the reverse * order of creation, so this failure cannot happen. */ hashtable->skewBucket[bucketToRemove] = NULL; hashtable->nSkewBuckets--; pfree(bucket); hashtable->spaceUsed -= SKEW_BUCKET_OVERHEAD; hashtable->spaceUsedSkew -= SKEW_BUCKET_OVERHEAD; /* * If we have removed all skew buckets then give up on skew optimization. * Release the arrays since they aren't useful any more. */ if (hashtable->nSkewBuckets == 0) { hashtable->skewEnabled = false; pfree(hashtable->skewBucket); pfree(hashtable->skewBucketNums); hashtable->skewBucket = NULL; hashtable->skewBucketNums = NULL; hashtable->spaceUsed -= hashtable->spaceUsedSkew; hashtable->spaceUsedSkew = 0; } }