mirror of https://github.com/postgres/postgres
bucket number, so as to ensure locality of access to the index during the insertion step. Without this, building an index significantly larger than available RAM takes a very long time because of thrashing. On the other hand, sorting is just useless overhead when the index does fit in RAM. We choose to sort when the initial index size exceeds effective_cache_size. This is a revised version of work by Tom Raney and Shreya Bhargava.REL8_5_ALPHA1_BRANCH
Tom Lane
18 years ago
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/*-------------------------------------------------------------------------
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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) 1996-2008, 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 1.1 2008/03/16 23:15:08 tgl 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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