[HBASE-20674] clean up short circuit read logic and docs

• Type: Bug
• Status: Patch Available
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 2.0.0
• Component/s: regionserver
• Assignee: Unassigned
• Reporter: Mike Drob
• Created: 02/Jun/18 01:58
• Updated: 15/Feb/22 01:16

Description

Mailing list discussion at https://lists.apache.org/thread.html/f6f73df0ceae29f762f9b9088e3ffd0bf8f109d3dd692df100bf4fd6@%3Cdev.hbase.apache.org%3E

There are several inconsistencies between how our docs claim we do things and how we actually do things.

There are two docs sections that attempt to address how SCR should work.

dfs.client.read.shortcircuit.skip.checksum is advised to set to true, but our code in separate places ignores it and then later sets it to true anyway.

CommonFSUtils and FSUtils duplicate code related to SCR setup.

There is a workaround in HFileSystem for a bug that's been fixed in all versions of hadoop that we support. (HADOOP-9307)

We suggest setting dfs.client.read.shortcircuit.buffer.size to a value that is very close to what we'd set it to anyway, without clearly explaining why this is important.

There are other properties that we claim are important, but we don't offer any suggestions or explanations.