Log Message:
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1. Improve tuplesort.c to support variable merge order. The original coding
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.
2. Improve sorting speed by pre-extracting the first sort-key column of
each tuple, as per my proposal of several days ago. Also, clean up
sort memory management by keeping all working data in a separate memory
context, and refine the handling of low-memory conditions.
Simon Riggs with some rework by Tom Lane
Modified Files:
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bizgres/postgresql/src/backend/utils/sort:
tuplesort.c (r1.1.1.3.2.1 -> r1.2)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/bizgres/bizgres/postgresql/src/backend/utils/sort/tuplesort.c.diff?r1=1.1.1.3.2.1&r2=1.2)