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From "Yu Li (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-14623) Implement dedicated WAL for system tables
Date Fri, 20 May 2016 02:30:13 GMT

    [ https://issues.apache.org/jira/browse/HBASE-14623?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15292576#comment-15292576
] 

Yu Li commented on HBASE-14623:
-------------------------------

Bumping up the timeout may still not work under some corner case, say wal with namespace data
at the end of the split queue. And current implementation seems to indicate namespace table
is necessary to be online and will abort master if wait timeout:
{code:title=TableNamespaceManager#start|borderStyle=solid}
    try {
      // Wait for the namespace table to be initialized.
      long startTime = EnvironmentEdgeManager.currentTime();
      int timeout = conf.getInt(NS_INIT_TIMEOUT, DEFAULT_NS_INIT_TIMEOUT);
      while (!isTableAvailableAndInitialized()) {
        if (EnvironmentEdgeManager.currentTime() - startTime + 100 > timeout) {
          // We can't do anything if ns is not online.
          throw new IOException("Timedout " + timeout + "ms waiting for namespace table to
"
              + "be assigned and enabled: " + getTableState());
        }
        Thread.sleep(100);
      }
    } catch (InterruptedException e) {
      throw (InterruptedIOException) new InterruptedIOException().initCause(e);
    }
{code}

> 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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