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由 Omer Arap 提交于
GPORCA should not spend time extracting column statistics that are not needed for cardinality estimation. This commit eliminates this overhead of requesting and generating the statistics for columns that are not used in cardinality estimation unnecessarily. E.g: `CREATE TABLE foo (a int, b int, c int);` For table foo, the query below only needs for stats for column `a` which is the distribution column and column `c` which is the column used in where clause. `select * from foo where c=2;` However, prior to that commit, the column statistics for column `b` is also calculated and passed for the cardinality estimation. The only information needed by the optimizer is the `width` of column `b`. For this tiny information, we transfer every stats information for that column. This commit and its counterpart commit in GPDB ensures that the column width information is passed and extracted in the `dxl:Relation` metadata information. Preliminary results for short running queries provides up to 65x performance improvement. Signed-off-by: NJemish Patel <jpatel@pivotal.io>
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