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MDEV-16934 Query with very large IN clause lists runs slowly

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This patch introduces support for the system variable eq_range_index_dive_limit
that existed in MySQL starting from 5.6. The variable sets a limit for
index dives into equality ranges. Index dives are performed by optimizer
to estimate the number of rows in range scans. Index dives usually provide
good estimate but they are pretty expensive. To estimate the number of rows
in equality ranges statistical data on indexes can be employed. Its usage gives
not so good estimates but it's cheap. So if the number of equality dives
required by an index scan exceeds the set limit no dives for equality
ranges are performed by the optimizer for this index.

As the new system variable is introduced in a stable version the default
value for it is set to a special value meaning there is no limit for the number
of index dives performed by the optimizer.

The patch partially uses the MySQL code for WL 5957
'Statistics-based Range optimization for many ranges'.
This commit is contained in:
Igor Babaev
2018-08-17 14:27:42 -07:00
parent d6f7fd6016
commit 4eac5df3fc
13 changed files with 239 additions and 19 deletions
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6
mysql-test/r/mysqld--help.result
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@ -197,6 +197,11 @@ The following specify which files/extra groups are read (specified before remain
cache, etc)
--enforce-storage-engine=name
Force the use of a storage engine for new tables
--eq-range-index-dive-limit=#
The optimizer will use existing index statistics instead
of doing index dives for equality ranges if the number of
equality ranges for the index is larger than or equal to
this number. If set to 0, index dives are always used.
--event-scheduler[=name]
Enable the event scheduler. Possible values are ON, OFF,
and DISABLED (keep the event scheduler completely
@ -1259,6 +1264,7 @@ encrypt-binlog FALSE
encrypt-tmp-disk-tables FALSE
encrypt-tmp-files FALSE
enforce-storage-engine (No default value)
eq-range-index-dive-limit 0
event-scheduler OFF
expensive-subquery-limit 100
expire-logs-days 0