Himanshu Vashishtha created HBASE-8346:
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Summary: Prefetchiing .META. rows in case only when useCache is
set to true
Key: HBASE-8346
URL: https://issues.apache.org/jira/browse/HBASE-8346
Project: HBase
Issue Type: Bug
Components: Client
Affects Versions: 0.95.0
Reporter: Himanshu Vashishtha
Priority: Minor
While doing a .META. lookup (HCM#locateRegionInMeta), we also prefetch some
other region's info for that table. The usual call to the meta lookup has
useCache variable set to true.
Currently, it calls preFetch irrespective of the value useCache flag:
{code}
if (Bytes.equals(parentTable, HConstants.META_TABLE_NAME) &&
(getRegionCachePrefetch(tableName))) {
prefetchRegionCache(tableName, row);
}
{code}
Later on, if useCache flag is set to false, it deletes the entry for that row
from the cache with a forceDeleteCachedLocation() call. This always results in
two calls to the .META. table in this case. The useCase variable is set to
false in case we are retrying to find a region (regionserver failover).
It can be verified from the log statements of a client while having a
regionserver failover. In the below example, the client was connected to a1217,
when a1217 got killed. The region in question is moved to a1215. Client got
this info from META scan, where as client cache this info from META, but then
delete it from cache as it want the latest info.
The result is even the meta provides the latest info, it is still deleted This
causes even the latest info to be deleted.
{code}
13/04/15 09:49:12 DEBUG client.HConnectionManager$HConnectionImplementation:
Cached location for
t,user7225973201630273569,1365536809331.40382355b8c45e1338d620c018f8ff6c. is
a1217.abc.com:40020
13/04/15 09:49:12 WARN client.ServerCallable: Received exception, tries=1,
numRetries=30 message=Connection refused
13/04/15 09:49:12 DEBUG client.HConnectionManager$HConnectionImplementation:
Removed all cached region locations that map to
a1217.abc.com,40020,1365621947381
13/04/15 09:49:13 DEBUG client.MetaScanner: Current INFO from scan results =
{NAME =>
't,user7225973201630273569,1365536809331.40382355b8c45e1338d620c018f8ff6c.',
STARTKEY => 'user7225973201630273569', ENDKEY => '', ENCODED =>
40382355b8c45e1338d620c018f8ff6c,}
13/04/15 09:49:13 DEBUG client.MetaScanner: Scanning .META. starting at
row=t,user7225973201630273569,00000000000000 for max=10 rows using
hconnection-0x7786df0f
13/04/15 09:49:13 DEBUG client.MetaScanner: Current INFO from scan results =
{NAME =>
't,user7225973201630273569,1365536809331.40382355b8c45e1338d620c018f8ff6c.',
STARTKEY => 'user7225973201630273569', ENDKEY => '', ENCODED =>
40382355b8c45e1338d620c018f8ff6c,}
13/04/15 09:49:13 DEBUG client.HConnectionManager$HConnectionImplementation:
Cached location for
t,user7225973201630273569,1365536809331.40382355b8c45e1338d620c018f8ff6c. is
*a1215.abc.com:40020*
13/04/15 09:49:13 DEBUG client.HConnectionManager$HConnectionImplementation:
*Removed a1215.abc.com:40020* as a location of
t,user7225973201630273569,1365536809331.40382355b8c45e1338d620c018f8ff6c. for
tableName=t from cache
13/04/15 09:49:13 DEBUG client.MetaScanner: Current INFO from scan results =
{NAME =>
't,user7225973201630273569,1365536809331.40382355b8c45e1338d620c018f8ff6c.',
STARTKEY => 'user7225973201630273569', ENDKEY => '', ENCODED =>
40382355b8c45e1338d620c018f8ff6c,}
13/04/15 09:49:13 DEBUG client.HConnectionManager$HConnectionImplementation:
Cached location for
t,user7225973201630273569,1365536809331.40382355b8c45e1338d620c018f8ff6c. is
*a1215.abc.com:40020*
13/04/15 09:49:13 WARN client.ServerCallable: Received exception, tries=2,
numRetries=30
message=org.apache.hadoop.hbase.exceptions.UnknownScannerException: Name:
-6313340536390503703, already closed?
13/04/15 09:49:13 DEBUG client.ClientScanner: Advancing internal scanner to
startKey at 'user760712450403198900'
{code}
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