[HBASE-12411] Optionally enable p-reads and private readers for compactions

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 0.98.9, 0.99.2
• Component/s: Performance

Release Note

This introduces two new configuration options:
# hbase.storescanner.use.pread enables postional reads for all scanners (except compactions). Default off (i.e. try to use seek+read as before)
# hbase.regionserver.compaction.private.readers has compaction run with their own readers. Default off (i.e. share readers with all other scanners as before)

• Assignee: Lars Hofhansl
• Reporter: Lars Hofhansl
• Created: 03/Nov/14 05:56
• Updated: 06/Apr/18 17:54
• Resolved: 18/Nov/14 22:15

Description

In the light of HDFS-6735 we might want to consider refraining from seek + read completely and only perform preads.

For example currently a compaction can lock out every other scanner over the file which the compaction is currently reading for compaction.

At the very least we can introduce an option to avoid seek + read, so we can allow testing this in various scenarios.
This will definitely be of great importance for projects like Phoenix which parallelize queries intra region (and hence readers will used concurrently by multiple scanner with high likelihood.)