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https://issues.apache.org/jira/browse/ACCUMULO-550?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13404130#comment-13404130
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Keith Turner commented on ACCUMULO-550:
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I do not think having the blocks > level 0 sprinkled through between level 0
blocks is a problem for sequentially reading the index. The blocks > level 0
are read so infrequently compared to the level 0 blocks that I suspect the cost
of the occasional random read for a level 1 block is amortized away.
> Collocate rfile index entries within file
> -----------------------------------------
>
> Key: ACCUMULO-550
> URL: https://issues.apache.org/jira/browse/ACCUMULO-550
> Project: Accumulo
> Issue Type: Improvement
> Components: tserver
> Reporter: Keith Turner
> Assignee: Keith Turner
> Fix For: 1.5.0, 1.4.1
>
>
> Before multi-level indexes were introduced, when an an rfile was written its
> entire index was held in memory and written out then the file was closed.
> With the introduction of multilevel index each index block is written when it
> fills up as the file is being written. This was done to handle the case
> where the index may not fit into memory. This leads to index blocks being
> sprinkled through the file. So any operation that iterates over the entire
> index can be slow because it turns into a lot of random accesses.
> One possible solution is to buffer lots of index blocks up to some some
> threshold and write out alot of index blocks at once. This would make a scan
> of the index much faster as it would turn into a set of sequential reads of
> large chunks of data.
> Could buffer all block at a particular level and write them out when the
> parent index block fills up.
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