[PHOENIX-3744] Support snapshot scanners for MR-based queries

• Type: New Feature
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 4.11.0
• Assignee: Akshita Malhotra
• Reporter: James R. Taylor
• Created: 17/Mar/17 22:44
• Updated: 01/Aug/23 14:18
• Resolved: 10/Jun/17 01:34

Description

HBase support scanning over snapshots, with a SnapshotScanner that accesses the region directly in HDFS. We should make sure that Phoenix can support that.

Not sure how we'd want to decide when to run a query over a snapshot. Some ideas:

• if there's an SCN set (i.e. the query is running at a point in time in the past)
• if the memstore is empty
• if the query is being run at a timestamp earlier than any memstore data
• as a config option on the table
• as a query hint
• based on some kind of optimizer rule (i.e. based on estimated # of bytes that will be scanned)

Phoenix typically runs a query at the timestamp at which it was compiled. Any data committed after this time should not be seen while a query is running.

Issue Links

• depends upon: PHOENIX-3820 Refactor Region Observer functionality (PHOENIX) to fetch processed region scanner without coprocessor environment
• links to: GitHub Pull Request #239
• links to: GitHub Pull Request #239
• links to: GitHub Pull Request #255
• links to: GitHub Pull Request #255
• links to: Support snapshot scanner for MR-based queries