I am trying to come up with a locking hierarchy document for all the locks
used in HBase. Any details/feedback anybody can share to make this document
better
would be much appreciated. This heirarchy can be used to interpreted as: a
thread that has a lock C cannot acquire A or B, and so on.
A. HRegionServer.lock
This lock protects the list of regions maintained by a region server.
The lock protects a data structure called onlineRegions that mantains a
map of region names to HRegion.
Question: what is region quiesce?
B. HRegion.newScannerLock
This lock ensures that puts and deletes are atomic. Also, one cannot
close
a region unless all puts, deletes and scans are completed.
put gets a writelock
delete gets a writelock
scanner gets a readlock
regionclose gets a writelock
flushcache gets a writelock to switch between memstore
and new store files
C. HRegion.splitsAndClosesLock
This lock ensures that compactions and flshCaches are completed before
a region close is successful. I do not yet understand why put and delete
have to acquire this lock.
put gets a readlock to check if record already exists
delete gets a readlock
compaction gets a readlock
flushCache gets a readlock
regionclose gets a writelock
D. RowLock
This is for atomic updates of a row.
put gets a rowlock
E. HRegion.updatesLock
put gets a readlock to insert entire key into memstore and
hlog
delete gets a readlock
interalFlushCache gets a writelock to snapshot memstore and
hlog
F. HRegion.synchronized_splitLock
G. HRegion.synchronized_writestate
H. MemStore.lock
I. Store.compactLock
compaction gets a writelock: allows only 1 compaction at a time
J. Store.lock
add(KeyValue) gets a readlock
delete(KeyValue) gets a readlock
get(KeyValue) gets a readlock
close gets a writelock
completeCompaction gets a writelock
---------------------------------------------
One posible problem lock hierarchy violation:
HRegion.flushcache holds the splitsAndClosesLock.readlock and then invokes
internalFlushCache. internalFlushCache acquires the netScannerLock to
switch
between memstore and new store files. could this cause a problem?
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