[ACCUMULO-2889] Batch metadata table updates for new walogs

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Incomplete
• Affects Version/s: 1.5.1, 1.6.0
• Assignee: Jonathan Park
• Reporter: Jonathan Park
• Created: 10/Jun/14 20:49
• Updated: 09/Jul/15 22:50
• Resolved: 09/Jul/15 22:50

Description

Currently, when we update the Metadata table with new loggers, we will update the metadata for each tablet serially. We could optimize this to instead use a batchwriter to send all metadata updates for all tablets in a batch.

A few special cases include:

• What if the !METADATA tablet was included in the batch?
• What about the root tablet?

Benefit:
In one of our clusters, we're experiencing particularly slow HDFS operations leading to large oscillations in ingest performance. We haven't isolated the cause in HDFS but when we profile the tservers, we noticed that they were waiting for metadata table operations to complete. This would target the waiting.

Potential downsides:
Given the existing locking scheme, it looks like we may have to lock a tablet for slightly longer (we'll lock for the duration of the batch).

Issue Links

• is related to: ACCUMULO-1294 Use batchwriter for MetadataTable.addDeleteEntries
• relates to: ACCUMULO-3423 speed up WAL roll-overs
• links to: review