[jira] [Commented] (HBASE-16649) Truncate table with splits preserved can cause both data loss and truncated data appeared again

[Allan Yang (JIRA)]

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https://issues.apache.org/jira/browse/HBASE-16649?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15502490#comment-15502490
 ] 

Allan Yang commented on HBASE-16649:
------------------------------------

Another thing is that we should change the seqid in master even if the new one 
is smaller than the old one, better have some redundant data when replay than 
lose them, right?
{code:java}
if (existingValue == null || (l != HConstants.NO_SEQNUM && l > existingValue)) {
        flushedSequenceIdByRegion.put(encodedRegionName, l);
      } else if (l != HConstants.NO_SEQNUM && l < existingValue) {
        flushedSequenceIdByRegion.put(encodedRegionName, l);  //update the 
seqid but log a warning
        LOG.warn("RegionServer " + sn + " indicates a last flushed sequence id 
("
            + l + ") that is less than the previous last flushed sequence id ("
            + existingValue + ") for region " + Bytes.toString(entry.getKey()) 
+ " Ignoring.");
      }
{code}

> Truncate table with splits preserved can cause both data loss and truncated 
> data appeared again
> -----------------------------------------------------------------------------------------------
>
>                 Key: HBASE-16649
>                 URL: https://issues.apache.org/jira/browse/HBASE-16649
>             Project: HBase
>          Issue Type: Bug
>    Affects Versions: 1.1.3
>            Reporter: Allan Yang
>         Attachments: HBASE-16649-v0.patch
>
>
> Since truncate table with splits preserved will delete hfiles and use the 
> previous regioninfo. It can cause odd behaviors
> - Case 1: *Data appeared after truncate*
> reproduce procedure：
> 1. create a table, let's say 'test'
> 2. write data to 'test', make sure memstore of 'test' is not empty
> 3. truncate 'test' with splits preserved
> 4. kill the regionserver hosting the region(s) of 'test'
> 5. start the regionserver, now it is the time to witness the miracle! the 
> truncated data appeared in table 'test'
> - Case 2: *Data loss*
> reproduce procedure:
> 1. create a table, let's say 'test'
> 2. write some data to 'test', no matter how many
> 3. truncate 'test' with splits preserved
> 4. restart the regionserver to reset the seqid
> 5. write some data, but less than 2 since we don't want the seqid to run over 
> the one in 2
> 6. kill the regionserver hosting the region(s) of 'test'
> 7. restart the regionserver. Congratulations! the data writen in 4 is now all 
> lost
> *Why?*
> for case 1
> Since preserve splits in truncate table procedure will not change the 
> regioninfo, when log replay happens, the 'unflushed' data will restore back 
> to the region
> for case 2
> since the flushedSequenceIdByRegion are stored in Master in a map with the 
> region's encodedName. Although the table is truncated, the region's name is 
> not changed since we chose to preserve the splits. So after truncate the 
> table, the region's sequenceid is reset in the regionserver, but not reset in 
> master. When flush comes and report to master, master will reject the update 
> of sequenceid since the new one is smaller than the old one. The same happens 
> in log replay, all the edits writen in 4 will be skipped since they have a 
> smaller seqid



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