From f313457af5e9c55f2b6a7f7ef6e9ce4b02b1525c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sa=C5=A1a=20=C5=BDivkov?= <sasa.zivkov@sap.com>
Date: Tue, 9 Feb 2016 11:42:46 +0100
Subject: [PATCH] Make H2 database cache size configurable

H2 database by default uses up to the half of the amount of memory
available for the virtual machine (Runtime.getRuntime().maxMemory())
as described in [1]. In some cases this could contribute to an
out-of-memory error in Gerrit.

Introduce a new configuration parameter cache.h2CacheSize to limit
the H2 memory cache size. In this change this parameter is applied
to all persistent caches.

[1] http://www.h2database.com/html/features.html#cache_settings

Change-Id: I0217d4114f528275ca4094e0f3414ef23af80677
---
 Documentation/config-gerrit.txt                    | 14 ++++++++++++++
 .../gerrit/server/cache/h2/H2CacheFactory.java     | 12 ++++++++++--
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/Documentation/config-gerrit.txt b/Documentation/config-gerrit.txt
index 3dda56cfce..0968c40cfc 100644
--- a/Documentation/config-gerrit.txt
+++ b/Documentation/config-gerrit.txt
@@ -528,6 +528,20 @@ If not absolute, the path is resolved relative to `$site_path`.
 +
 Default is unset, no disk cache.
 
+[[cache.h2CacheSize]]cache.h2CacheSize::
++
+The size of the H2 database cache, in bytes, used for each persistent cache.
+This can be used to limit the H2 cache size and thus prevent out-of-memory
+caused by the H2 database using too much memory.
++
+Technically the H2 cache size is configured using the CACHE_SIZE parameter in
+the H2 JDBC connection URL, as described
+link:http://www.h2database.com/html/features.html#cache_settings[here]
++
+Default is unset, no cache size limit.
++
+Common unit suffixes of 'k', 'm', or 'g' are supported.
+
 [[cache.name.maxAge]]cache.<name>.maxAge::
 +
 Maximum age to keep an entry in the cache. Entries are removed from
diff --git a/gerrit-cache-h2/src/main/java/com/google/gerrit/server/cache/h2/H2CacheFactory.java b/gerrit-cache-h2/src/main/java/com/google/gerrit/server/cache/h2/H2CacheFactory.java
index fcacf78631..3ffb76c2d7 100644
--- a/gerrit-cache-h2/src/main/java/com/google/gerrit/server/cache/h2/H2CacheFactory.java
+++ b/gerrit-cache-h2/src/main/java/com/google/gerrit/server/cache/h2/H2CacheFactory.java
@@ -58,6 +58,7 @@ class H2CacheFactory implements PersistentCacheFactory, LifecycleListener {
   private final DynamicMap<Cache<?, ?>> cacheMap;
   private final ExecutorService executor;
   private final ScheduledExecutorService cleanup;
+  private final long h2CacheSize;
 
   @Inject
   H2CacheFactory(
@@ -68,6 +69,7 @@ class H2CacheFactory implements PersistentCacheFactory, LifecycleListener {
     defaultFactory = defaultCacheFactory;
     config = cfg;
     cacheDir = getCacheDir(site, cfg.getString("cache", null, "directory"));
+    h2CacheSize = cfg.getLong("cache", null, "h2CacheSize", -1);
     caches = Lists.newLinkedList();
     this.cacheMap = cacheMap;
 
@@ -220,8 +222,14 @@ class H2CacheFactory implements PersistentCacheFactory, LifecycleListener {
       TypeLiteral<K> keyType,
       long maxSize,
       Long expireAfterWrite) {
-    String url = "jdbc:h2:" + cacheDir.resolve(name).toUri();
-    return new SqlStore<>(url, keyType, maxSize,
+    StringBuilder url = new StringBuilder();
+    url.append("jdbc:h2:").append(cacheDir.resolve(name).toUri());
+    if (h2CacheSize >= 0) {
+      url.append(";CACHE_SIZE=");
+      // H2 CACHE_SIZE is always given in KB
+      url.append(h2CacheSize / 1024);
+    }
+    return new SqlStore<>(url.toString(), keyType, maxSize,
         expireAfterWrite == null ? 0 : expireAfterWrite.longValue());
   }
 }