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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-13291) Lift the scan ceiling
Date Mon, 30 Mar 2015 21:43:55 GMT

    [ https://issues.apache.org/jira/browse/HBASE-13291?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14387468#comment-14387468
] 

stack commented on HBASE-13291:
-------------------------------

# The vint mvcc on end of keyvalue is expensive to parse; we can't make use of the unsafe
toLong which seems a good deal faster than get bytes and bit noodling going by micro-benchmarking
(I see 10x diff doing unsafe #getLong over get byte and left shifting). This fact and the
way we have tags tagged on end (perhaps) frustrates go-fast efforts.
# Doing a getLong instead of two getInts and then bit noodling is faster than doing two getInts
(this is using unsafe -- I saw almost 10x diff). Added it in.
# Bulk of our time is in StoreFileScanner#_next
# Next is ScanQueryMatcher#match. It is not being very smart. It uses the Cell Interface to
pull out elements to compare only each getXXXoffset or getXXXlength starts over from scratch
reparsing key, value, row, etc. lengths extracting ints so as to do some offset math. This
is a killer.The worst offender is the call from #match to #isCellTTLExpired In here we check
to see if tags are enabled. We do this by parsing key and value ints to figure end of KV to
poke for tags. All scans are paying for that time when DLR sets an MVCC on a KV.
# If lots of cells being returned, then we will be doing lots of array resizing. These show
in the profilings.

The HFileReaderV3 and then HFileReaderV2 with an abstract under this makes it hard to navigate
what is going on. Need to flatten now we are up on v3 file format and all is on by default.

> Lift the scan ceiling
> ---------------------
>
>                 Key: HBASE-13291
>                 URL: https://issues.apache.org/jira/browse/HBASE-13291
>             Project: HBase
>          Issue Type: Improvement
>          Components: Scanners
>    Affects Versions: 1.0.0
>            Reporter: stack
>            Assignee: stack
>         Attachments: 13291.inlining.txt, Screen Shot 2015-03-26 at 12.12.13 PM.png, Screen
Shot 2015-03-26 at 3.39.33 PM.png, hack_to_bypass_bb.txt, nonBBposAndInineMvccVint.txt, q
(1).png, traces.7.svg, traces.filterall.svg, traces.nofilter.svg, traces.small2.svg, traces.smaller.svg
>
>
> Scanning medium sized rows with multiple concurrent scanners exhibits interesting 'ceiling'
properties. A server runs at about 6.7k ops a second using 450% of possible 1600% of CPUs
 when 4 clients each with 10 threads doing scan 1000 rows.  If I add '--filterAll' argument
(do not return results), then we run at 1450% of possible 1600% possible but we do 8k ops
a second.
> Let me attach flame graphs for two cases. Unfortunately, there is some frustrating dark
art going on. Let me try figure it... Filing issue in meantime to keep score in.



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