Reduce number of ZooCache instances and Watchers #5183
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This commit removes most of the places where ZooCache
instances were being created in favor of re-using the
ZooCache from the ClientContext. Additionally, this
commit does not place a Watcher on each node that is
cached and instead places a single persistent
recursive Watcher at the paths in which the caching
is taking place.
This change roughly reduces the Watchers reported in
WatchTheWatchCountIT by 50%. While reducing the number
of Watchers, this commit could reduce ZooKeeper server
performance in two ways:
1. There is a note in the ZooKeeper javadoc for the
AddWatchMode enum that states there is a small
performance decrease when using recursive watchers
as all of the segments of ZNode paths need to be
checked for watch triggering.
2. Because a Watcher is not set on each node this
commit modified the ZooCache.ZCacheWatcher to
remove the parent of the triggered node, the
triggered node, and all of its siblings from the
cache. This overmatching may mean increased
lookups in ZooKeeper.
Related to apache#5134
Closes apache#5154, apache#5157
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This commit removes most of the places where ZooCache instances were being created in favor of re-using the ZooCache from the ClientContext. Additionally, this commit does not place a Watcher on each node that is cached and instead places a single persistent recursive Watcher at the paths in which the caching is taking place.
This change roughly reduces the Watchers reported in WatchTheWatchCountIT by 50%. While reducing the number of Watchers, this commit could reduce ZooKeeper server performance in two ways:
There is a note in the ZooKeeper javadoc for the AddWatchMode enum that states there is a small performance decrease when using recursive watchers as all of the segments of ZNode paths need to be checked for watch triggering.
Because a Watcher is not set on each node this commit modified the ZooCache.ZCacheWatcher to remove the parent of the triggered node, the triggered node, and all of its siblings from the cache. This overmatching may mean increased lookups in ZooKeeper.
Related to #5134
Closes #5154, #5157