mmiklavc opened a new pull request #1483: METRON-2217 Migrate current HBase client from HTableInterface to Table URL: https://github.com/apache/metron/pull/1483 ## Contributor Comments https://issues.apache.org/jira/browse/METRON-2217 I want to get this in front of people to start reviewing asap. It's going to take me a couple days to work through a reasonable test plan for this, but this should not hold up reviewing the approach. Of note is that the change from HTableInterface to Table by HBase has now shifted the burden of connection management from the HTable implementation to the end user/client. We previously had very little, if any, hooks to close our HBase tables or attempt to clean up resources. In response to this change, there were a couple options for dealing with this: 1. Completely rewrite our HBase client logic to fully manage connection lifecycle 2. Isolate the connection management change to the existing HTableProvider implementation used throughout Metron and make a smaller, incremental change to set us up for the eventual upgrade to HBase 2.x. This PR takes the approach in option 2. The biggest question surrounding this approach is whether the included connection management changes introduced in the TableProvider are sufficient, or if we need to immediately take a more robust connection pooling approach to dealing with HBase connections. I spent some time looking at the current HTable implementation that we depend on. Every time an HTable is created, the underlying code makes a call to an internal connection manager. It's unclear to me what the connection management contract is for the user in this case, e.g. stale connection cleanup, connection retries, connection pooling, etc. This is probably the riskiest part of this change. The way that I'm handling this is to 1. Make the connections thread safe through use of a ThreadLocal connection variable. There are issues with instantiating a ThreadLocal variable by default in code that will be serialized by Storm. ThreadLocal is not serializable. In order to get around a massive API rewrite that would add initialization similar to our other startup hooks, e.g. StellarFunctions.initialize(), I opted for an approach that would allow us to get a similar effect via lazy initialization. 2. Providing some basic connection retry logic that will initiate a new connection if the thread's current connection happens to have closed for whatever reason. The combination of these 2 options provides a semi-robust way to handle connections without boiling the ocean as well as offering per-thread connection re-use that should limit the overall number of connections we keep open to HBase in a reasonable and reliable way. ## Pull Request Checklist Thank you for submitting a contribution to Apache Metron. 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