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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-14623) Implement dedicated WAL for system tables
Date Tue, 22 Mar 2016 18:19:25 GMT

    [ https://issues.apache.org/jira/browse/HBASE-14623?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15206953#comment-15206953
] 

stack commented on HBASE-14623:
-------------------------------

I just saw this. Thank you for contextualizing the issue. It helps situate what the change
is about and helps wth review. Up to this, this information has been coming in piecemeal and
seems to be made of disjoint quotes of yours which does not help.

My thing is this is a significant change around our assign. It should be on, not an option,
if it does as is claimed. I would like to see evidence posted that the purported benefits
actually hold under cluster test if we are going to make such a significant change. Ditto
on evidence/timing on how assign changes with these extra WALs in the mix.

Would also like to avoid code/function/concept duplication (this bit where we have system
tables and then hbase:meta needs to be fixed... hbase:meta was the original system table...
)

Just looking for the basics....

> Implement dedicated WAL for system tables
> -----------------------------------------
>
>                 Key: HBASE-14623
>                 URL: https://issues.apache.org/jira/browse/HBASE-14623
>             Project: HBase
>          Issue Type: Sub-task
>          Components: wal
>            Reporter: Ted Yu
>            Assignee: Ted Yu
>              Labels: wal
>             Fix For: 2.0.0
>
>         Attachments: 14623-v1.txt, 14623-v2.txt, 14623-v2.txt, 14623-v2.txt, 14623-v2.txt,
14623-v3.txt, 14623-v4.txt
>
>
> As Stephen suggested in parent JIRA, dedicating separate WAL for system tables (other
than hbase:meta) should be done in new JIRA.
> This task is to fulfill the system WAL separation.
> Below is summary of discussion:
> For system table to have its own WAL, we would recover system table faster (fast log
split, fast log replay). It would probably benefit 
> AssignmentManager on system table region assignment. At this time, the new AssignmentManager
is not planned to change WAL. So the existence of this JIRA is good for overall system, not
specific to AssignmentManager.
> There are 3 strategies for implementing system table WAL:
> 1. one WAL for all non-meta system tables
> 2. one WAL for each non-meta system table
> 3. one WAL for each region of non-meta system table
> Currently most system tables are one region table (only ACL table may become big). Choices
2 and 3 basically are the same.
> From implementation point of view, choices 2 and 3 are cleaner than choice 1 (as we have
already had 1 WAL for META table and we can reuse the logic). With choice 2 or 3, assignment
manager performance should not be impacted and it would be easier for assignment manager to
assign system table region (eg. without waiting for user table log split to complete for assigning
system table region).



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