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Use column collation for extended statistics

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The current extended statistics code was a bit confused which collation
to use.  When building the statistics, the collations defined as default
for the data types were used (since commit 5e0928005).  The MCV code was
however using the column collations for MCV serialization, and then
DEFAULT_COLLATION_OID when computing estimates. So overall the code was
using all three possible options, inconsistently.

This uses the column colation everywhere - this makes it consistent with
what 5e0928005 did for regular stats.  We however do not track the
collations in a catalog, because we can derive them from column-level
information.  This may need to change in the future, e.g. after allowing
statistics on expressions.

Reviewed-by: Tom Lane
Discussion: https://postgr.es/m/8736jdhbhc.fsf%40ansel.ydns.eu
Backpatch-to: 12
This commit is contained in:
Tomas Vondra
2019-07-18 12:28:16 +02:00
parent e38a55ba46
commit a63378a03e
4 changed files with 17 additions and 6 deletions
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2
src/backend/statistics/mvdistinct.c
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@@ -477,7 +477,7 @@ ndistinct_for_combination(double totalrows, int numrows, HeapTuple *rows,
colstat->attrtypid);
/* prepare the sort function for this dimension */
multi_sort_add_dimension(mss, i, type->lt_opr, type->typcollation);
multi_sort_add_dimension(mss, i, type->lt_opr, colstat->attrcollid);
/* accumulate all the data for this dimension into the arrays */
for (j = 0; j < numrows; j++)