[HBASE-5504] Online Merge

• Type: Brainstorming
• Status: Closed
• Priority: Major
• Resolution: Duplicate
• Affects Version/s: 0.94.0
• Component/s: Client, master, shell, Zookeeper
• Assignee: Unassigned
• Reporter: Mubarak Seyed
• Created: 01/Mar/12 23:28
• Updated: 13/Jun/22 15:35
• Resolved: 29/Jan/13 03:41

Description

As discussed, please refer the discussion at HBASE-4991

Design suggestion from Stack:

I suggest a design below. It has some prerequisites, some general function that this feature could use (and others). The prereqs if you think them good, could be done outside of this JIRA.

Here's a suggested rough outline of how I think this feature should run. The feature I'm describing below is merge and deleteRegion for I see them as in essence the same thing.

(C) Client, (M) Master, RS (Region server), ZK (ZooKeeper)

1. Client calls merge or deleteRegion API. API is a range of rows. (C)
2. Master gets call. (M)
3. Master obtains a write lock on table so it can't be disabled from under us. The write lock will also disable splitting. This is one of the prereqs I think. Its HBASE-5494 (Or we could just do something simpler where we have a flag up in zk that splitRegion checks but thats less useful I think; OR we do the dynamic configs issue and set splits to off via a config. change). There'd be a timer for how long we wait on the table lock. (M -> ZK)
4. If we get the lock, write intent to merge a range up into zk. It also hoists into zk if its a pure merge or a merge that drops the region data (a deleteRegion call) (M)
5. Return to the client either our failed attempt at locking the table or an id of some sort used identifying this running operation; can use it querying status. (M -> C)
6. Turn off balancer. TODO/prereq: Do it in a way that is persisted. Balancer switch currently in memory only so if master crashes, new master will come up in balancing mode # (If we had dynamic config. could hoist up to zk a config. that disables the balancer rather than have a balancer-specific flag/znode OR if a write lock outstanding on a table, then the balancer does not balance regions in the locked table - this latter might be the easiest to do) (M)
7. Write into zk that just turned off the balancer (If it was on) (M -> ZK)
8. Get regions that are involved in the span (M)
9. Hoist the list up into zk. (M -> ZK)
10. Create region to span the range. (M)
11. Write that we did this up into zk. (M -> ZK)
12. Close regions in parallel. Confirm close in parallel. (M -> RS)
13. Write up into zk regions closed (This might not be necessary since can ask if region is open). (M -> ZK)
14. If a merge and not a delete region, move files under new region. Might multithread this (moves should go pretty fast). If a deleteregion, we skip this step. (M)
15. On completion mark zk (though may not be necessary since its easy to look in fs to see state of move). (M -> ZK)
16. Edit .META. (M)
17. Confirm edits went in. (M)
18. Move old regions to hbase trash folder TODO: There is no trash folder under /hbase currently. We should add one. (M)
19. Enable balancer (if it was off) (M)
20. Unlock table (M)

Issue Links

• depends upon: HBASE-5494 Introduce a zk hosted table-wide read/write lock so only one table operation at a time
• is related to: HBASE-1621 merge tool should work on online cluster
• is related to: HBASE-7403 Online Merge
• is related to: HBASE-5459 Provide capability to find the status of Master coordinated tasks
• relates to: HBASE-3887 Add region deletion tool