#At file:///home/rl136806/mysql/repo/mysql-work4/ based on revid:roy.lyseng@stripped
3394 Roy Lyseng 2011-06-27
Bug#11752543: Prepared query with nested subqueries core dump on second exec.
Also known as bug#43768
The problem here is that pullout of semi-join tables is attempted for
each execution, but because those tables are not "pushed back" again
after each execution, the pullout fails on second attempt.
The solution chosen here is to pullout only those semi-join tables that are
functionally dependent upon the outer tables. This pullout operation
need to be performed only once, and, unlike the current procedure, is not
dependent upon the row count of the involved tables.
Pullout of semi-join tables based on rowcount (tables that we know
contain exactly zero or one rows) is abandoned all together.
The practical implication of this change is as follows:
- Only outer tables containing zero or one rows will now be extracted
as "const tables". Thus, such tables from a semijoin nest are no
longer accessed during optimization, and some (rare) optimizations
are no longer possible.
- In the majority of cases, there is no performance impact. Often,
the new strategy chosen is Materialization, meaning that the row
of these table is accessed only once and saved in local memory.
Whether it is accessed during optimization or execution should not
affect performance.
- Const table analysis is now done in two phases:
1) Extract tables based on dependencies. Both regular and semi-joined
tables may apply, and
2) Extract tables based on row count. Semi-joined tables are not
handled in this phase.
In order to implement this, make_join_statistics() has been restructured
slightly. The conditional logic within the function has also been
enhanced for better readability.
The logic of make_join_statistics() is now as follows:
1. Initialize JOIN data structures
(major part of first loop in existing implementation).
2. Update dependencies based on join information
(the Warshall algorithm).
3. Make key descriptions (update_ref_and_keys()).
4. Pull out semi-join tables based on identified dependencies,
called only during the first optimization.
5. Extract tables with zero or one rows as const tables
(Semi-joined tables are not handled).
6. Extract dependent tables as const tables.
(Semi-joined tables are not handled).
7. The remaining parts of the function.
mysql-test/include/subquery_sj.inc
Added test case for bug#11752543.
Extended "join loop" with prepared statement testing.
mysql-test/r/select_found.result
Possible keys changed from "PRIMARY,kid" to "kid".
Happens because analysis order is slightly changed, but harmless as
the table is identified as "const".
mysql-test/r/subquery_mat_all.result
Plan changes because const table pullout is removed for semi-join
tables.
mysql-test/r/subquery_sj_all.result
mysql-test/r/subquery_sj_all_jcl6.result
mysql-test/r/subquery_sj_all_jcl7.result
mysql-test/r/subquery_sj_dupsweed.result
mysql-test/r/subquery_sj_dupsweed_jcl6.result
mysql-test/r/subquery_sj_dupsweed_jcl7.result
mysql-test/r/subquery_sj_firstmatch.result
mysql-test/r/subquery_sj_firstmatch_jcl6.result
mysql-test/r/subquery_sj_firstmatch_jcl7.result
mysql-test/r/subquery_sj_loosescan.result
mysql-test/r/subquery_sj_loosescan_jcl6.result
mysql-test/r/subquery_sj_loosescan_jcl7.result
mysql-test/r/subquery_sj_mat.result
mysql-test/r/subquery_sj_mat_jcl6.result
mysql-test/r/subquery_sj_mat_jcl7.result
mysql-test/r/subquery_sj_mat_nosj.result
mysql-test/r/subquery_sj_none.result
mysql-test/r/subquery_sj_none_jcl6.result
mysql-test/r/subquery_sj_none_jcl7.result
Added test case for bug#11752543
A number of plan changes because of extensive testing of semi-join
tables with 0, 1 and 2 rows.
sql/sql_select.cc
pull_out_semijoin_tables()
Pullout based on const tables removed.
Comments updated.
make_join_statistics()
Removed const table pullout from first loop.
Simplified testing based on inner/outer/semi-join properties.
Calls pull_out_semijoin_tables() just after dependency analysis.
Then, added loop that performs pullout based on row count
but excludes semi-joined tables.
Notice also that we no longer delete outer-join dependencies
based on row count. This has some implications for EXPLAIN, but
all plans are still the same.
modified:
mysql-test/include/subquery_sj.inc
mysql-test/r/select_found.result
mysql-test/r/subquery_mat_all.result
mysql-test/r/subquery_sj_all.result
mysql-test/r/subquery_sj_all_jcl6.result
mysql-test/r/subquery_sj_all_jcl7.result
mysql-test/r/subquery_sj_dupsweed.result
mysql-test/r/subquery_sj_dupsweed_jcl6.result
mysql-test/r/subquery_sj_dupsweed_jcl7.result
mysql-test/r/subquery_sj_firstmatch.result
mysql-test/r/subquery_sj_firstmatch_jcl6.result
mysql-test/r/subquery_sj_firstmatch_jcl7.result
mysql-test/r/subquery_sj_loosescan.result
mysql-test/r/subquery_sj_loosescan_jcl6.result
mysql-test/r/subquery_sj_loosescan_jcl7.result
mysql-test/r/subquery_sj_mat.result
mysql-test/r/subquery_sj_mat_jcl6.result
mysql-test/r/subquery_sj_mat_jcl7.result
mysql-test/r/subquery_sj_mat_nosj.result
mysql-test/r/subquery_sj_none.result
mysql-test/r/subquery_sj_none_jcl6.result
mysql-test/r/subquery_sj_none_jcl7.result
sql/sql_select.cc
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| Thread |
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| • bzr commit into mysql-trunk branch (roy.lyseng:3394) Bug#11752543 | Roy Lyseng | 27 Jun |
