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authorMichal Schmidt <mschmidt@redhat.com>2014-12-09 20:27:19 +0100
committerMichal Schmidt <mschmidt@redhat.com>2014-12-09 21:43:34 +0100
commitb7c88ab8cc7d55a43450bf3dea750f95f2e910d6 (patch)
tree253914fdcb32ab6bda4482ec832d01fa4b8c13ec /units/initrd.target
parent1372d5eff4631aeec132b8e22d243fb81a4fdbc8 (diff)
journal: optimize iteration: skip whole files behind current location
Interleaving of entries from many journal files is expensive. But there is room for optimization. We can skip looking into journal files whose entries all lie before the current iterating location. We can tell if that's the case from looking at the journal file header. This saves a huge amount of work if one has many of mostly not interleaved journal files. On my workstation with 90 journal files in /var/log/journal/ID/ totalling 3.4 GB I get these results: Before: $ time ./journalctl --since=2014-06-01 --until=2014-07-01 > /dev/null real 5m54.258s user 2m4.263s sys 3m48.965s After: $ time ./journalctl --since=2014-06-01 --until=2014-07-01 > /dev/null real 0m20.518s user 0m19.989s sys 0m0.328s The high "sys" time in the original was caused by putting more stress on the mmap-cache than it could handle. With the patch the working set now consists of fewer mmap windows and mmap-cache is not thrashing.
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