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https://issues.apache.org/jira/browse/HBASE-12031?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14145386#comment-14145386
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Vladimir Rodionov commented on HBASE-12031:
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[[email protected]]
{quote}
You are adding a HFIleReaderContext. We have a HFileContext already. You cannot
reuse/amend this class to your purposes?
{quote}
HFileContext carries the information on some of the meta data about the HFile -
this is per HFile. FielReaderContext is per Reader (Scanner).
{quote}
I would not expect a Context to do the actual reading as in + public boolean
read(long offset, byte[] buffer, int bufOffset, int len). I could imagine
passing in a context when you read.
{quote}
Probably, yes but need a place (class) to move the actual read to.
{quote}
Regards read-ahead and keeping the buffer local to the scanner, it is not
enough just having the scanner do a read-ahead that ensures blockcache is
populated? You have to bring the data local to the scanner? If multiple
concurrent scans, we'll have duplicate data buffered?
{quote}
Not sure how to implement this. Not all data from read ahead buffer should be
cached in a general case. Sharing some data between scanners in RA buffer is
not a common case.
{quote}
Hard to see what you did in readAtOffset.
{quote}
If scanner is in *pread* mode - execute OLD code for *pread*
else
if read -ahead disabled (context == null) - execute OLD code
else if streaming lock enabled - execute OLD code
else ( Read ahead enabled && streaming lock - not enabled) - execute NEW code:
Check if we can server block from RA buffer - if yes - read & return block,
otherwise read ahead next buffer, read block and return.
> Parallel Scanners inside Region
> -------------------------------
>
> Key: HBASE-12031
> URL: https://issues.apache.org/jira/browse/HBASE-12031
> Project: HBase
> Issue Type: New Feature
> Components: Performance, Scanners
> Affects Versions: 0.98.6
> Reporter: Vladimir Rodionov
> Assignee: Vladimir Rodionov
> Fix For: 1.0.0, 2.0.0, 0.98.7, 0.99.1
>
> Attachments: HBASE-12031.2.patch, HBASE-12031.3.patch,
> HBASE-12031.patch, ParallelScannerDesign.pdf, hbase-12031-tests.tar.gz
>
>
> This JIRA to improve performance of multiple scanners running on a same
> region in parallel. The scenarios where we will get the performance benefits:
> * New TableInputFormat with input splits smaller than HBase Region.
> * Scanning during compaction (Compaction scanner and application scanner over
> the same Region).
> Some JIRAs related to this one:
> https://issues.apache.org/jira/browse/HBASE-7336
> https://issues.apache.org/jira/browse/HBASE-5979
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