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https://issues.apache.org/jira/browse/HBASE-9870?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13811081#comment-13811081
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stack commented on HBASE-9870:
------------------------------

[~anoop.hbase] for my understanding, when you say 'the existing data', do you 
mean data that has already been loaded into the block cache or do you mean 
something else?  (Changing the encoding, you have to offline the region?).  Or 
is 'existing data' something else?  Won't the data in hfiles be properly 
converted from old encoding to new?   Thanks.

> HFileDataBlockEncoderImpl#diskToCacheFormat uses wrong format
> -------------------------------------------------------------
>
>                 Key: HBASE-9870
>                 URL: https://issues.apache.org/jira/browse/HBASE-9870
>             Project: HBase
>          Issue Type: Bug
>            Reporter: Jimmy Xiang
>
> In this method, we have
> {code}
>     if (block.getBlockType() == BlockType.ENCODED_DATA) {
>       if (block.getDataBlockEncodingId() == onDisk.getId()) {
>         // The block is already in the desired in-cache encoding.
>         return block;
>       }
> {code}
> This assumes onDisk encoding is the same as that of inCache.  This is not 
> true when we change the encoding of a CF.  This could be one of the reasons I 
> got data loss with online encoding change?
> If I make sure onDisk == inCache all the time, my ITBLL with online encoding 
> change worked once for me.



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