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https://issues.apache.org/jira/browse/HBASE-9870?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13811072#comment-13811072
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Anoop Sam John commented on HBASE-9870:
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Yes this is to avoid a decode and then encode in the read path which is costly.
At any point of time there can be only same type of encoding for OnDisk and
InCache for a CF. (If OnDisk != None)
But when we alter the encoding for a CF!!! Yes at time also both in cache and
on disk are same.. But the existing data!!! On disk that can be in another
encoding format.. So this is an issue.
Very good finding Jimmy..
> 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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