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Improve tuplesort.c to support variable merge order. The original coding

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with fixed merge order (fixed number of "tapes") was based on obsolete
assumptions, namely that tape drives are expensive.  Since our "tapes"
are really just a couple of buffers, we can have a lot of them given
adequate workspace.  This allows reduction of the number of merge passes
with consequent savings of I/O during large sorts.

Simon Riggs with some rework by Tom Lane
This commit is contained in:
Tom Lane
2006-02-19 05:54:06 +00:00
parent 85c0eac1af
commit df700e6b40
3 changed files with 169 additions and 63 deletions
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4
src/include/utils/tuplesort.h
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@@ -13,7 +13,7 @@
* Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/utils/tuplesort.h,v 1.17 2004/12/31 22:03:46 pgsql Exp $
* $PostgreSQL: pgsql/src/include/utils/tuplesort.h,v 1.18 2006/02/19 05:54:06 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -67,6 +67,8 @@ extern bool tuplesort_getdatum(Tuplesortstate *state, bool forward,
extern void tuplesort_end(Tuplesortstate *state);
extern int tuplesort_merge_order(long allowedMem);
/*
* These routines may only be called if randomAccess was specified 'true'.
* Likewise, backwards scan in gettuple/getdatum is only allowed if