53 lines
1.7 KiB
MySQL
53 lines
1.7 KiB
MySQL
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-- Copyright 2018 Tanel Poder. All rights reserved. More info at http://tanelpoder.com
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-- Licensed under the Apache License, Version 2.0. See LICENSE.txt for terms & conditions.
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-- count(columnX) is slower than count(*) or count(1)
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drop table t;
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create table t cache as select * from v$session;
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insert into t select * from t;
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insert into t select * from t;
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insert into t select * from t;
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insert into t select * from t;
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insert into t select * from t;
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insert into t select * from t;
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insert into t select * from t;
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insert into t select * from t;
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insert into t select * from t;
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insert /*+ append */ into t select * from t;
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commit;
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insert /*+ append */ into t select * from t;
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commit;
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insert /*+ append */ into t select * from t;
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commit;
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insert /*+ append */ into t select * from t;
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commit;
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insert /*+ append */ into t select * from t;
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commit;
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insert /*+ append */ into t select * from t;
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commit;
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exec dbms_stats.gather_table_stats(user, 'T');
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-- to get better rowsource level timing accuracy
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alter session set "_rowsource_statistics_sampfreq"=1;
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select /*+ gather_plan_statistics */ count(*) from t;
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set timing on
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select /*+ gather_plan_statistics */ count(*) from t;
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select * from table(dbms_xplan.display_cursor(null,null,'ALLSTATS LAST'));
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select /*+ gather_plan_statistics */ count(1) from t;
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select * from table(dbms_xplan.display_cursor(null,null,'ALLSTATS LAST'));
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select /*+ gather_plan_statistics */ count(sid) from t;
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select * from table(dbms_xplan.display_cursor(null,null,'ALLSTATS LAST'));
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select /*+ gather_plan_statistics */ count(state) from t;
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select * from table(dbms_xplan.display_cursor(null,null,'ALLSTATS LAST'));
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-- set back to default
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alter session set "_rowsource_statistics_sampfreq"=128;
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