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Added comment #2770

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Alexey Milovidov 2018-09-19 23:22:58 +03:00
parent b396818632
commit 68a4ad0034
1 changed files with 5 additions and 0 deletions
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dbms/src/Functions/FunctionsDateTime.h
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@ -1592,6 +1592,11 @@ public:
* - low number of arithmetic ops due to pre-filled pattern; * - low number of arithmetic ops due to pre-filled pattern;
* - for somewhat reason, function by pointer call is faster than switch/case. * - for somewhat reason, function by pointer call is faster than switch/case.
* *
* Possible further optimization options:
* - slightly interleave first and second step for better cache locality
* (but it have no sense when character array fits L1d cache);
* - avoid indirect function calls and inline functions with JIT compilation.
*
* Performance on Intel(R) Core(TM) i7-6700 CPU @ 3.40GHz: * Performance on Intel(R) Core(TM) i7-6700 CPU @ 3.40GHz:
* *
* WITH formatDateTime(now() + number, '%H:%M:%S') AS x SELECT count() FROM system.numbers WHERE NOT ignore(x); * WITH formatDateTime(now() + number, '%H:%M:%S') AS x SELECT count() FROM system.numbers WHERE NOT ignore(x);