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117 lines
2.9 KiB
C
117 lines
2.9 KiB
C
/*-------------------------------------------------------------------------
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*
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* hashsort.c
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* Sort tuples for insertion into a new hash index.
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*
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* When building a very large hash index, we pre-sort the tuples by bucket
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* number to improve locality of access to the index, and thereby avoid
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* thrashing. We use tuplesort.c to sort the given index tuples into order.
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*
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* Note: if the number of rows in the table has been underestimated,
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* bucket splits may occur during the index build. In that case we'd
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* be inserting into two or more buckets for each possible masked-off
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* hash code value. That's no big problem though, since we'll still have
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* plenty of locality of access.
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*
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*
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* Portions Copyright (c) 1996-2009, 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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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/access/hash/hashsort.c,v 1.2 2009/01/01 17:23:35 momjian Exp $
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include "access/hash.h"
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#include "miscadmin.h"
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#include "utils/tuplesort.h"
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/*
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* Status record for spooling/sorting phase.
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*/
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struct HSpool
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{
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Tuplesortstate *sortstate; /* state data for tuplesort.c */
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Relation index;
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};
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/*
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* create and initialize a spool structure
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*/
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HSpool *
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_h_spoolinit(Relation index, uint32 num_buckets)
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{
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HSpool *hspool = (HSpool *) palloc0(sizeof(HSpool));
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uint32 hash_mask;
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hspool->index = index;
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/*
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* Determine the bitmask for hash code values. Since there are currently
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* num_buckets buckets in the index, the appropriate mask can be computed
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* as follows.
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*
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* Note: at present, the passed-in num_buckets is always a power of 2,
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* so we could just compute num_buckets - 1. We prefer not to assume
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* that here, though.
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*/
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hash_mask = (((uint32) 1) << _hash_log2(num_buckets)) - 1;
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/*
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* We size the sort area as maintenance_work_mem rather than work_mem to
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* speed index creation. This should be OK since a single backend can't
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* run multiple index creations in parallel.
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*/
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hspool->sortstate = tuplesort_begin_index_hash(index,
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hash_mask,
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maintenance_work_mem,
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false);
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return hspool;
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}
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/*
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* clean up a spool structure and its substructures.
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*/
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void
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_h_spooldestroy(HSpool *hspool)
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{
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tuplesort_end(hspool->sortstate);
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pfree(hspool);
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}
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/*
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* spool an index entry into the sort file.
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*/
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void
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_h_spool(IndexTuple itup, HSpool *hspool)
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{
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tuplesort_putindextuple(hspool->sortstate, itup);
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}
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/*
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* given a spool loaded by successive calls to _h_spool,
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* create an entire index.
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*/
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void
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_h_indexbuild(HSpool *hspool)
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{
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IndexTuple itup;
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bool should_free;
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tuplesort_performsort(hspool->sortstate);
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while ((itup = tuplesort_getindextuple(hspool->sortstate,
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true, &should_free)) != NULL)
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{
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_hash_doinsert(hspool->index, itup);
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if (should_free)
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pfree(itup);
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}
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}
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