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From "Duo Zhang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-17712) Remove/Simplify the logic of RegionScannerImpl.handleFileNotFound
Date Wed, 01 Mar 2017 13:34:45 GMT

    [ https://issues.apache.org/jira/browse/HBASE-17712?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15890163#comment-15890163

Duo Zhang commented on HBASE-17712:

This not [~tedyu]'s fault. Skimmed the comments in HBASE-16304, I do not think he knew the
reason why we call dropMemstoreContents() for increment and append either. He just follow
the old behavior. We can refreshStoreFiles in handleFileNotFound, and refreshStoreFiles will
call dropMemstoreContents before HBASE-16304. And in append and increment we acquire write
lock so it could lead to a dead lock then he moved the dropMemstoreContents out of write lock
protection. The dropMemstoreContents is part of refreshStoreFiles, we split it into two pieces
to avoid dead lock.

'refreshStoreFiles' is designed to be used by secondary replica only, and we reuse it in HBASE-13651
to handle FileNotFoundException. This is the root cause.

> Remove/Simplify the logic of RegionScannerImpl.handleFileNotFound
> -----------------------------------------------------------------
>                 Key: HBASE-17712
>                 URL: https://issues.apache.org/jira/browse/HBASE-17712
>             Project: HBase
>          Issue Type: Bug
>    Affects Versions: 2.0.0, 1.4.0
>            Reporter: Duo Zhang
>             Fix For: 2.0.0, 1.4.0
> It is introduced in HBASE-13651 and the logic became much more complicated after HBASE-16304
due to a dead lock issue. It is really tough as sequence id is involved in and the method
we called is used to serve secondary replica originally which does not handle write.
> In fact, in 1.x release, the problem described in HBASE-13651 is gone. Now we will write
a compaction marker to WAL before deleting the compacted files. We can only consider a RS
as dead after its WAL files are all closed so if the region has already been reassigned the
compaction will fail as we can not write out the compaction marker.
> So theoretically, if we still hit FileNotFound exception, it should be a critical bug
which means we may loss data. I do not think it is a good idea to just eat the exception and
refresh store files. Or even if we want to do this, we can just refresh store files without
dropping memstore contents. This will also simplify the logic a lot.
> Suggestions are welcomed.

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