Add LICENSE and README.md files Changes: * LICENSE contains the standard 'Apache License Version 2.0' * README.md contains necessary information on how to build and setup Gerrit and gerrit-cached-refdb library module Change-Id: Icbb57bef63f13e3762a0b636f5c510d8741d5f2f
diff --git a/LICENSE b/LICENSE new file mode 100644 index 0000000..11069ed --- /dev/null +++ b/LICENSE
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diff --git a/README.md b/README.md new file mode 100644 index 0000000..c539da7 --- /dev/null +++ b/README.md
@@ -0,0 +1,88 @@ +# Plugin to cache Git repository's access to refdb + +When [Serialize AccountCache series](https://gerrit-review.googlesource.com/c/gerrit/+/260992) +was introduced it simplified the cache eviction by always reaching out to JGit +for data. Unfortunately it comes with +[price](https://bugs.chromium.org/p/gerrit/issues/detail?id=14945) +which is especially high when *All-Users* repository is accessed through the +NFS and `core.trustFolderStat = false` is configured in +`${GERRIT_SITE}/etc/jgit.config` (quite common setup for HA/Multi-Site ens). + +This plugin was developed to introduce the in-memory cache (managed by Gerrit +so that evictions could be coordinated to multiple nodes) that reduces the +price for reaching to refs in JGit. It is a Gerrit native alternative (that can +be applied to Gerrit 3.2) to work that is currently under progress for +[caching Refs in JGit](https://git.eclipse.org/r/c/jgit/jgit/+/186205). + +Here is the short comparison of _heavy-refs-related_ operations performance. +The test scenario was to get random change details (over the same REST API that +is used in Gerrit's details page) in 8 parallel threads over 5mins period of +time. The `core.trustFolderStat = false` was set in +`${GERRIT_SITE}/etc/jgit.config`. +It was called against: +* vanilla Gerrit 3.1.16 version (marked as `stable-3.1` in the results) +* vanilla Gerrit 3.2.12 version (marked as `stable-3.2` in the results) +* Gerrit 3.2.14 with libCache module loaded (marked as `stable-3.2-libCache` in + the results). + +Note that `TRS` is `Reqs/Sec` for each Thread. + +--- +| version | TRS Avg | TRS Std Dev | TRS Max | Total Reqs/sec | Transfer/sec(MB)| +| -- | -- | -- | -- | -- | -- | +| stable-3.1 | 57,33 | 8,26 | 80 | 456,95 | 4,34 | +| stable-3.2 | 13,87 | 4,92 | 20 | 110,18 | 1,07 | +| stable-3.2-libCache | 105,27 | 14,55 | 150 | 834,88 | 8,41 | +| stable-3.1 vs stable-3.2 | 313,34% | 67,89% | 300,00% | 314,73% | 305,61% | +| stable-3.2-libCache vs stable-3.2 | 658,98% | 195,73% | 650,00% | 657,74% | 685,98% | +| stable-3.2-libCache vs stable-3.1 | 83,62% | 76,15% | 87,50% | 82,71% | 93,78% | +--- + +One can clearly see that in this setup using this library module outperforms both +Gerrit 3.2 and 3.1 by factor of *6* and *2* correspondingly. +The test script, detailed description and more results are available +[here](https://gist.github.com/geminicaprograms/b2cae199793f0f2b18759a803000447f). + +## How to build + +Clone or link this plugin to the plugins directory of Gerrit's source tree, +and then run bazel build on the plugin's directory. + +Example: + +``` +git clone --recursive https://gerrit.googlesource.com/gerrit +cd plugins +git clone "https://review.gerrithub.io/geminicaprograms/gerrit-cached-refdb" +cd .. && bazel build plugins/gerrit-cached-refdb +``` + +The output plugin jar is created in: + +``` +bazel-bin/plugins/gerrit-cached-refdb/gerrit-cached-refdb.jar +``` + +## How to install + +Copy the gerrit-cached-refdb.jar into the `${GERRIT_SITE}/lib/` so that it is +being loaded when the Gerrit instance is started. Note that the following +configuration options need to be added + +``` +git config --file ${GERRIT_SITE}/etc/gerrit.config gerrit.installDbModule\ + com.googlesource.gerrit.plugins.gerritcachedrefdb.LibDbModule +git config --file ${GERRIT_SITE}/etc/gerrit.config gerrit.installModule\ + com.googlesource.gerrit.plugins.gerritcachedrefdb.LibSysModule +``` + +By default cache can hold up to `1024` refs which will not be sufficient for +any production site therefore one can configure it through the standard Gerrit +cache configuration means e.g. + +``` +git config --file ${GERRIT_SITE}/etc/gerrit.config cache.ref_by_name.memoryLimit 10240 +``` + +Note that libraty module requires the Gerrit instance restart in order to pick +up the configuration changes. \ No newline at end of file