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From "Matteo Bertozzi (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-17140) Throw RegionOfflineException directly when request for a disabled table
Date Mon, 28 Nov 2016 18:53:58 GMT

    [ https://issues.apache.org/jira/browse/HBASE-17140?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15702781#comment-15702781
] 

Matteo Bertozzi commented on HBASE-17140:
-----------------------------------------

can you expand more on why we should do this optimization? do you have a use specific case?
my guess is that disabling a table is rare enough and extra round trips are not that bad...

then if we are going with this patch, why do we even need to store the enabled/disabled table
state? if we know that all the regions are offline we know that the table is disabled. and
the master can simply compute the state when rebuilding meta on startup. so there is really
no need to have that flag stored. 

also i'm not sure if we have enough coverage to cover the behavior of setting the offline
state for disable. at the moment we only use the offline flag for split/merge. and the regions
may be back if we rollback. so maybe this is not a trivial change. our code has lots of assumptions
and changing things from TableNotEnabledException to RegionOfflineException feels scary to
me.

> Throw RegionOfflineException directly when request for a disabled table
> -----------------------------------------------------------------------
>
>                 Key: HBASE-17140
>                 URL: https://issues.apache.org/jira/browse/HBASE-17140
>             Project: HBase
>          Issue Type: Improvement
>          Components: Client
>            Reporter: Guanghao Zhang
>            Assignee: Guanghao Zhang
>         Attachments: HBASE-17140-v1.patch, HBASE-17140-v2.patch, HBASE-17140-v3.patch,
HBASE-17140-v4.patch, HBASE-17140-v5.patch
>
>
> Now when request for a disabled table, it need 3 rpc calls before fail.
> 1. get region location
> 2. send call to rs and get NotServeRegionException
> 3. retry and check the table state, then throw TableNotEnabledException
> The table state check is added for disabled table. But now the prepare method in RegionServerCallable
shows that all retry request will get table state first.
> {code}
> public void prepare(final boolean reload) throws IOException {
>     // check table state if this is a retry
>     if (reload && !tableName.equals(TableName.META_TABLE_NAME) &&
>         getConnection().isTableDisabled(tableName)) {
>       throw new TableNotEnabledException(tableName.getNameAsString() + " is disabled.");
>     }
>     try (RegionLocator regionLocator = connection.getRegionLocator(tableName)) {
>       this.location = regionLocator.getRegionLocation(row);
>     }
>     if (this.location == null) {
>       throw new IOException("Failed to find location, tableName=" + tableName +
>           ", row=" + Bytes.toString(row) + ", reload=" + reload);
>     }
>     setStubByServiceName(this.location.getServerName());
> }
> {code}
> An improvement is set the region offline in HRegionInfo. Then throw the RegionOfflineException
when get region location.
> Review board: https://reviews.apache.org/r/54071/



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