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Commit3d3a81f

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Fix tuple_fraction calculation in generate_orderedappend_paths()
6b94e7a adjusted generate_orderedappend_paths() to consider fractionalpaths. However, it didn't manage to interpret the tuple_fraction valuecorrectly. According to the header comment of grouping_planner(), thetuple_fraction >= 1 specifies the absolute number of expected tuples. Thatnumber must be divided by the expected total number of tuples to get theactual fraction.Even though this is a bug fix, we don't backpatch it. The risks of the sideeffects of plan changes on stable branches are too high.Reported-by: Andrei Lepikhov <lepihov@gmail.com>Discussion:https://postgr.es/m/3ca271fa-ca5c-458c-8934-eb148622b270%40gmail.comAuthor: Andrei Lepikhov <lepihov@gmail.com>Reviewed-by: Junwang Zhao <zhjwpku@gmail.com>Reviewed-by: Alvaro Herrera <alvherre@alvh.no-ip.org>Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
1 parent12eee85 commit3d3a81f

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3 files changed

+32
-1
lines changed

3 files changed

+32
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lines changed

‎src/backend/optimizer/path/allpaths.c

Lines changed: 11 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1891,7 +1891,17 @@ generate_orderedappend_paths(PlannerInfo *root, RelOptInfo *rel,
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*/
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if (root->tuple_fraction>0)
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{
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doublepath_fraction= (1.0 /root->tuple_fraction);
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doublepath_fraction=root->tuple_fraction;
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/*
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* Merge Append considers only live children relations. Dummy
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* relations must be filtered out before.
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*/
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Assert(childrel->rows>0);
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/* Convert absolute limit to a path fraction */
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if (path_fraction >=1.0)
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path_fraction /=childrel->rows;
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cheapest_fractional=
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get_cheapest_fractional_path_for_pathkeys(childrel->pathlist,

‎src/test/regress/expected/partition_join.out

Lines changed: 18 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -5260,6 +5260,24 @@ SELECT x.id, y.id FROM fract_t x LEFT JOIN fract_t y USING (id) ORDER BY x.id DE
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Index Cond: (id = x_2.id)
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(11 rows)
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EXPLAIN (COSTS OFF) -- Should use NestLoop with parameterised inner scan
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SELECT x.id, y.id FROM fract_t x LEFT JOIN fract_t y USING (id)
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ORDER BY x.id DESC LIMIT 2;
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QUERY PLAN
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--------------------------------------------------------------------------------
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Limit
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-> Merge Append
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Sort Key: x.id DESC
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-> Nested Loop Left Join
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-> Index Only Scan Backward using fract_t0_pkey on fract_t0 x_1
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-> Index Only Scan using fract_t0_pkey on fract_t0 y_1
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Index Cond: (id = x_1.id)
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-> Nested Loop Left Join
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-> Index Only Scan Backward using fract_t1_pkey on fract_t1 x_2
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-> Index Only Scan using fract_t1_pkey on fract_t1 y_2
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Index Cond: (id = x_2.id)
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(11 rows)
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--
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-- Test Append's fractional paths
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--

‎src/test/regress/sql/partition_join.sql

Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1224,6 +1224,9 @@ SELECT x.id, y.id FROM fract_t x LEFT JOIN fract_t y USING (id) ORDER BY x.id AS
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EXPLAIN (COSTS OFF)
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SELECTx.id,y.idFROM fract_t xLEFT JOIN fract_t y USING (id)ORDER BYx.idDESCLIMIT10;
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EXPLAIN (COSTS OFF)-- Should use NestLoop with parameterised inner scan
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SELECTx.id,y.idFROM fract_t xLEFT JOIN fract_t y USING (id)
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ORDER BYx.idDESCLIMIT2;
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--
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-- Test Append's fractional paths

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