Migration from H2 Caches

This module provides a REST API to help converting existing cache from H2 to chronicle-map, which requires the Administrate Server capability to be executed.

The migration must be executed before switching to use chronicle-map, while Gerrit cache is still backed by H2.

The migration can be run online without any disruption of the Gerrit server. However note that since the migration perform many, sequential reads from the H2 database, it will participate to the overall database load, so you should test accordingly.

The migration would do the following:

  1. scan all existing cache key-value pairs
  2. calculate the parameters for the new cache
  3. create the new cache
  4. read all existing key-value pairs and insert them into the new cache-chroniclemap files

The following caches will be migrated (if they exist and contain any data):

  • accounts
  • change_kind
  • change_notes
  • conflicts
  • diff
  • diff_intraline
  • diff_summary
  • git_tags
  • mergeability
  • oauth_token
  • persisted_projects
  • pure_revert
  • web_sessions

The migration should be performed as follows:

  • Copy cache-chroniclemap.jar file in the plugins/ directory.
  • Wait for the pluginLoader to load the new plugin. You will see an entry in the error_log:
INFO  com.google.gerrit.server.plugins.PluginLoader : Loaded plugin cache-chroniclemap
  • You can now run the migration
curl -v -XPUT -u <admin> '<gerrit>/a/plugins/cache-chroniclemap/migrate?[size-multiplier=FACTOR]&[bax-bloat-factor=MULTIPLIER]'

This might require some time, depending on the size of the H2 caches and it will terminate with the output of the configuration that should be places in etc/gerrit.configin order to leverage the newly created caches correctly.

Output example:

   [cache "diff"]
   	maxEntries = 216
   	avgKeySize = 188
   	avgValueSize = 796
   	maxBloatFactor = 1
   [cache "persisted_projects"]
   	maxEntries = 3
   	avgKeySize = 80
   	avgValueSize = 4087
   	maxBloatFactor = 1
   [cache "diff_summary"]
   	maxEntries = 216
   	avgKeySize = 192
   	avgValueSize = 254
   	maxBloatFactor = 1
   [cache "accounts"]
   	maxEntries = 2
   	avgKeySize = 52
   	avgValueSize = 194
   	maxBloatFactor = 1
   [cache "mergeability"]
   	maxEntries = 2444
   	avgKeySize = 150
   	avgValueSize = 20
   	maxBloatFactor = 1
   [cache "web_sessions"]
   	maxEntries = 94852
   	avgKeySize = 68
   	avgValueSize = 382
   	maxBloatFactor = 1

Optionally the REST endpoint can receive the following additional arguments:

  • max-bloat-factor=FACTOR

maximum number of times chronicle-map cache is allowed to grow in size. default:3

  • size-multiplier=MULTIPLIER Multiplicative factor for the number of entries allowed in chronicle-map. default:3