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From "stack (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-1644) [hbase] Compactions should not block updates
Date Wed, 15 Aug 2007 19:37:30 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-1644?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

stack updated HADOOP-1644:
--------------------------

    Attachment: non-blocking-compaction.patch

Here is a patch that reworks compactions.

HADOOP-1644 [hbase] Compactions should not block updates

Disentangles flushes and compactions; flushes can proceed while a
compaction is happening.  Also, don't compact unless we hit
compaction threshold: i.e. don't automatically compact on HRegion
startup so regions can come online the faster.

M src/contrib/hbase/conf/hbase-default.xml
    (hbase.hregion.compactionThreashold): Moved to be a hstore property
    as part of encapsulating compaction decision inside hstore.
M src/contrib/hbase/src/test/org/apache/hadoop/hbase/HBaseTestCase.java
    Refactored.  Moved here generalized content loading code that can
    be shared by tests.  Add to setup and teardown the setup and removal
    of local test dir (if it exists).
M src/contrib/hbase/src/test/org/apache/hadoop/hbase/TestCompare.java
    Added test of HStoreKey compare (It works other than one would at
    first expect).
M src/contrib/hbase/src/test/org/apache/hadoop/hbase/TestSplit.java
    Bulk of content loading code has been moved up into the parent class.
M src/contrib/hbase/src/java/org/apache/hadoop/hbase/HConnectionManager.java
    (tableExists): Restore to a check of if the asked-for table is in list of
    tables.  As it was, a check for tableExists would just wait on all timeouts
    and retries to expire and then report table does not exist..  Fixed up
    debug message listing regions of a table.  Added protection against meta
    table not having a COL_REGINFO (Seen in cluster testing -- probably a bug
    in row removal).
M src/contrib/hbase/src/java/org/apache/hadoop/hbase/HStoreFile.java
    Loading store files, even if it was noticed that there was no corresponding
    map file, was still counting file as valid.  Also fix merger -- was
    constructing MapFile.Reader directly rather than asking HStoreFile for
    the reader (HStoreFile knows how to do MapFile references)
    (rename): Added check that move succeeded and logging.  In cluster-testing,
    the hdfs move of compacted file into place has failed on occasion (Need
    more info).
M src/contrib/hbase/src/java/org/apache/hadoop/hbase/HStore.java
    Encapsulate ruling on whether a compaction should take place inside HStore.
    Added reading of the compactionThreshold her.  Compaction threshold is
    currently just number of store files.  Later may include other factors such
    as count of reference files.  Cleaned up debug messages around
    reconstruction log.  Removed compaction if size > 1 from constructor.  Let
    compaction happen after we've been deployed (Compactions that happen while
    we are online can continue to take updates.  Compaction in the constructor
    puts off our being able to take in updates).
    (close): Changed so it now returns set of store files.  This used to be done
    by calls to flush. Since flush and compaction have been disentangled, a
    compaction can come in after flush and the list of files could be off.
    Having it done by close, can be sure list of files is complete.
    (flushCache): No longer returns set of store files.  Added 'merging compaction'
    where we pick an arbitrary store file from disk and merge into it the content
    of memcache (Needs work).
    (getAllMapFiles): Renamed getAllStoreFiles.
    (needsCompaction): Added.
    (compactHelper): Added passing of maximum sequence number if already
    calculated. If compacting one file only, we used skip without rewriting
    the info file.  Fixed.
    Refactored.  Moved guts to new  compact(outFile, listOfStores)  method.
    (compact, CompactionReader): Added overrides and interface  to support
    'merging compaction' that takes files and memcache.  In compaction,
    if we failed the move of the compacted file, all data had already been
    deleted.  Changing, so deletion happens after confirmed move of
    compacted file.
    (getFull): Fixed bug where NPE when read of maps came back null.
    Revealed by our NOT compacting stores on startup.  Meant could be two
    backing stores one of which had no data regards queried key.
    (getNMaps): Renamed countOfStoreFiles.
    (toString): Added.
M src/contrib/hbase/src/java/org/apache/hadoop/hbase/HStoreKey.java
    Added comment on 'odd'-looking comparison.
M src/contrib/hbase/src/java/org/apache/hadoop/hbase/HRegionServer.java
    Javadoc edit. 
M src/contrib/hbase/src/java/org/apache/hadoop/hbase/HLogEdit.java
    Only return first 128 bytes of value when toStringing (On cluster,
    was returning complete web pages in log).
M src/contrib/hbase/src/java/org/apache/hadoop/hbase/HMaster.java
    Removed confusing debug message (made sense once -- but not now).
    Test rootRegionLocation for null before using it (can be null).
M  src/contrib/hbase/src/java/org/apache/hadoop/hbase/HMemcache.java
    Added comment that delete behavior needs study.
M src/contrib/hbase/src/java/org/apache/hadoop/hbase/HRegion.java
    Fixed merge so it doesn't do the incremental based off files
    returned by flush.  Instead all is done in the one go after
    region closes (using files returned by close).
    Moved duplicated code to new filesByFamily method.
    (WriteState): Removed writesOngoing in favor of compacting and
    flushing flags.
    (flushCache): No longer returns list of files.
M src/contrib/hbase/src/java/org/apache/hadoop/hbase/util/Writables.java
    Fix javadoc.

> [hbase] Compactions should not block updates
> --------------------------------------------
>
>                 Key: HADOOP-1644
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1644
>             Project: Hadoop
>          Issue Type: Improvement
>          Components: contrib/hbase
>    Affects Versions: 0.15.0
>            Reporter: stack
>            Assignee: stack
>             Fix For: 0.15.0
>
>         Attachments: interlacing.patch, non-blocking-compaction.patch
>
>
> Currently, compactions take a long time.  During compaction, updates are carried by the
HRegions' memcache (+ backing HLog).  memcache is unable to flush to disk until compaction
completes.
> Under sustained, substantial --  rows that contain multiple columns one of which is a
web page -- updates by multiple concurrent clients (10 in this case), a common hbase usage
scenario, the memcache grows fast and often to orders of magnitude in excess of the configured
'flush-to-disk' threshold.
> This throws the whole system out of kilter.  When memcache does get to run after compaction
completes -- assuming you have sufficent RAM and the region server doesn't OOME -- then the
resulting on-disk file will be way larger than any other on-disk HStoreFile bringing on a
region split ..... but the resulting split will produce regions that themselves need to be
immediately split because each half is beyond the configured limit, and so on...
> In another issue yet to be posted, tuning and some pointed memcache flushes makes the
above condition less extreme but until compaction durations come close to the memcache flush
threshold compactions will remain disruptive. 
> Its allowed that compactions may never be fast enough as per bigtable paper (This is
a 'wish' issue).

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