pgsql: Avoid O(N^2) behavior when enlarging SPI tuple table in spi_prin

Avoid O(N^2) behavior when enlarging SPI tuple table in spi_printtup().

For no obvious reason, spi_printtup() was coded to enlarge the tuple
pointer table by just 256 slots at a time, rather than doubling the size at
each reallocation, as is our usual habit. For very large SPI results, this
makes for O(N^2) time spent in repalloc(), which of course soon comes to
dominate the runtime. Use the standard doubling approach instead.

This is a longstanding performance bug, so back-patch to all active
branches.

Neil Conway

Branch
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REL9_5_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/68a14ca74be03ab189b83c2bbf0b68c5d1daba44

Modified Files
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src/backend/executor/spi.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)