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cb37c55768
Merge Facebook commit 154c579b828a60722a7d9477fc61868c07453d08 and e8f0052f9b112dc786bf9b957ed5b16a5749f7fd authored by Steaphan Greene from https://github.com/facebook/mysql-5.6 Optimize prefix index queries to skip cluster index lookup when possible. Currently InnoDB will always fetch the clustered index (primary key index) for all prefix columns in an index, even when the value of a particular record is smaller than the prefix length. This change optimizes that case to use the record from the secondary index and avoid the extra lookup. Also adds two status vars that track how effective this is: innodb_secondary_index_triggered_cluster_reads: Times secondary index lookup triggered cluster lookup. innodb_secondary_index_triggered_cluster_reads_avoided: Times prefix optimization avoided triggering cluster lookup.
103 lines
2.7 KiB
Plaintext
103 lines
2.7 KiB
Plaintext
drop table if exists prefixinno;
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set global innodb_prefix_index_cluster_optimization = ON;
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show variables like 'innodb_prefix_index_cluster_optimization';
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Variable_name Value
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innodb_prefix_index_cluster_optimization ON
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# Create a table with a large varchar field that we index the prefix
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# of and ensure we only trigger cluster lookups when we expect it.
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create table prefixinno (
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id int not null,
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fake_id int not null,
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bigfield varchar(4096),
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primary key(id),
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index bigfield_idx (bigfield(32)),
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index fake_id_bigfield_prefix (fake_id, bigfield(32))
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) engine=innodb;
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insert into prefixinno values (1, 1001, repeat('a', 1)),
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(8, 1008, repeat('b', 8)),
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(24, 1024, repeat('c', 24)),
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(31, 1031, repeat('d', 31)),
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(32, 1032, repeat('x', 32)),
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(33, 1033, repeat('y', 33)),
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(128, 1128, repeat('z', 128));
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select * from prefixinno;
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id fake_id bigfield
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1 1001 a
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8 1008 bbbbbbbb
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24 1024 cccccccccccccccccccccccc
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31 1031 ddddddddddddddddddddddddddddddd
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32 1032 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
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33 1033 yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy
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128 1128 zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz
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# Baseline sanity check: 0, 0.
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no-op query
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no-op query
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cluster_lookups_matched
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1
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cluster_lookups_avoided_matched
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1
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# Eligible for optimization.
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id bigfield
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31 ddddddddddddddddddddddddddddddd
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cluster_lookups_matched
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1
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cluster_lookups_avoided_matched
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1
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# Eligible for optimization, access via fake_id only.
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id bigfield
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31 ddddddddddddddddddddddddddddddd
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cluster_lookups_matched
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1
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cluster_lookups_avoided_matched
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1
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# Not eligible for optimization, access via fake_id of big row.
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id bigfield
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33 yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy
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cluster_lookups_matched
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1
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cluster_lookups_avoided_matched
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1
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# Not eligible for optimization.
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id bigfield
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32 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
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cluster_lookups_matched
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1
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cluster_lookups_avoided_matched
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1
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# Not eligible for optimization.
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id bigfield
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33 yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy
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cluster_lookups_matched
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1
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cluster_lookups_avoided_matched
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1
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# Eligible, should not increment lookup counter.
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id bigfield
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8 bbbbbbbb
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cluster_lookups_matched
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1
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cluster_lookups_avoided_matched
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1
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# Eligible, should not increment lookup counter.
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id bigfield
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24 cccccccccccccccccccccccc
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cluster_lookups_matched
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1
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cluster_lookups_avoided_matched
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1
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# Should increment lookup counter.
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id bigfield
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128 zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz
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cluster_lookups_matched
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1
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cluster_lookups_avoided_matched
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1
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# Disable optimization, confirm we still increment counter.
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id bigfield
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33 yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy
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cluster_lookups_matched
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1
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cluster_lookups_avoided_matched
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1
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# make test suite happy by cleaning up our mess
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