[ACCUMULO-2743] Improve stale-reads with ZooKeeper-backed data

• Type: Sub-task
• Status: Resolved
• Priority: Major
• Resolution: Incomplete
• Assignee: Unassigned
• Reporter: Josh Elser
• Created: 28/Apr/14 17:39
• Updated: 03/Sep/21 22:15
• Resolved: 03/Sep/21 22:15

Description

Writing test code against Accumulo, especially via MiniAccumuloCluster, can be extremely frustrating. ZooKeeper is used for managing table configurations, among other things, to allow all tabletservers to be aware of the state of a table.

The problem is that each tabletserver uses a Watcher to see when updates occur, and then it updates an internal cache of these properties. This is a problem even on an instance with a single tserver when setting a table property (configuring an iterator is a good example). The setTableProperty command is implemented via the Master, not a tserver like fetching the table configuration is implemented, which means that you're racing against the Watcher in the tserver.

The cause of this is that test code gets riddled with code like the following:

String myProperty = tableConfiguration.getProperty("myProperty");
for (int i = 0; i < retries && null == myProperty; i++) {
  myProperty = tableConfiguration.getProperty("myProperty");
  Thread.sleep(some_millis);
}
// Hope that you actually saw the update
Assert.assertNotNull(myProperty)

Issue Links

• is related to: ACCUMULO-4361 Test race conditions in ShellServerIT