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gerrit / gerrit / 4b9c5cb1a7fb272db2314380fa2b31282b4c1f91
commit4b9c5cb1a7fb272db2314380fa2b31282b4c1f91[log] [tgz]
authorHugo Arès <hugo.ares@ericsson.com>Fri Mar 24 17:48:33 2017 -0400
committerDavid Pursehouse <dpursehouse@collab.net>Wed Mar 29 03:09:55 2017 +0000
treec73f643a1e161ae22f476096dac777c990a1739b
parentf2d4fac3f35febc56fb6b64b482bfb35a4de9451 [diff]
Precompute h2 persisted cache space used per entry

The problem is h2 cannot execute concurrent queries on the same
database. The query to get the disk stats(count and space) is a long
lasting query which blocks any other queries to the same cache. The disk
stats are needed when pruning the cache (every day at 01:00) and when
caches are listed, either using the REST API or the show-caches ssh
command.

Here is an example of the problem: diff_intraline of 1GB limit with 1.6
million entries can take up to 16 seconds to compute disk stats. During
that time, any request that needs to get/insert data into the diff
intraline will be blocked until disk stats are done. Every time an admin
executes the show-caches command, a lot of requests can be blocked for a
long time; (number of big persisted caches) x (time to compute stats)

The problem is even worse during pruning because right after computing
the space, another long lasting query is executed; select every row and
associated space used.

Precomputing the space used improves the situation. In the previous
example, it reduces the query time from 16 to 4 seconds.

The real fix would be to also precompute the sum of space used by all
entries in a separate table but this is more complex since it would
involve triggers to keep the sum up to date when a row is inserted,
updated or deleted. Even with this, it would still not be perfect, in the
previous example, it reduces the query time from 4 to 2.5 seconds. The
number of rows also needs to be precomputed, but precomputing this would
be wrong since counting number of rows should be quick in a database; it
should not be implemented in the schema.

This change improves the situation by cutting the query time by 4 with
minimal change. A real fix will be done in another change.

Bug: Issue 5876
Change-Id: I38805688289a474aa719c52ab03079cbf11d1c5c
1 file changed
tree: c73f643a1e161ae22f476096dac777c990a1739b
  1. .settings/
  2. contrib/
  3. Documentation/
  4. gerrit-acceptance-framework/
  5. gerrit-acceptance-tests/
  6. gerrit-antlr/
  7. gerrit-cache-h2/
  8. gerrit-common/
  9. gerrit-elasticsearch/
  10. gerrit-extension-api/
  11. gerrit-gpg/
  12. gerrit-gwtdebug/
  13. gerrit-gwtexpui/
  14. gerrit-gwtui/
  15. gerrit-gwtui-common/
  16. gerrit-httpd/
  17. gerrit-launcher/
  18. gerrit-lucene/
  19. gerrit-main/
  20. gerrit-oauth/
  21. gerrit-openid/
  22. gerrit-patch-commonsnet/
  23. gerrit-patch-jgit/
  24. gerrit-pgm/
  25. gerrit-plugin-api/
  26. gerrit-plugin-gwtui/
  27. gerrit-prettify/
  28. gerrit-reviewdb/
  29. gerrit-server/
  30. gerrit-sshd/
  31. gerrit-test-util/
  32. gerrit-util-cli/
  33. gerrit-util-http/
  34. gerrit-util-ssl/
  35. gerrit-war/
  36. lib/
  37. plugins/
  38. polygerrit-ui/
  39. ReleaseNotes/
  40. tools/
  41. website/
  42. .bazelproject
  43. .editorconfig
  44. .git-blame-ignore-revs
  45. .gitignore
  46. .gitmodules
  47. .mailmap
  48. .pydevproject
  49. BUILD
  50. COPYING
  51. INSTALL
  52. README.md
  53. SUBMITTING_PATCHES
  54. version.bzl
  55. WORKSPACE
README.md

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