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https://issues.apache.org/jira/browse/HBASE-8701?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13679684#comment-13679684
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Sergey Shelukhin commented on HBASE-8701:
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bq. A MultiStoreFile would have edits from one WAL file for all regions in the
WAL? Which region would it live in and how would it get cleaned up? (When all
references had been dropped?) We'd have to write 'reference' files into each
region that pointed back to a range on this WAL? Wouldn't we be making near as
many NN operations as for the case where we wrote out an hfile per region?
It will have to use some form of links and references, and will have edits from
multiple stores. Something like that is described in BigTable paper actually :)
bq. I think this multistorefile notion too complex.
bq. We could keep hfiles per region in memory and not write them until we had
too but then we lose the incremental benefit and we start to arrive at the
Enis/Elliott scheme?
Why more complex? Should be pretty simple, we already have something like that.
Incremental benefit is auxiliary; main benefit in my view is precisely that we
don't have additional in-memory/file structures/separate memstores in the same
store that need to be reconciled/communication channels.
Agree on having seqIds for each KV... it will increase file size which is not a
huge deal probably, but will solve many problems. Should we do it now while we
are still before singularity?
> distributedLogReplay need to apply wal edits in the receiving order of those
> edits
> ----------------------------------------------------------------------------------
>
> Key: HBASE-8701
> URL: https://issues.apache.org/jira/browse/HBASE-8701
> Project: HBase
> Issue Type: Bug
> Components: MTTR
> Reporter: Jeffrey Zhong
> Assignee: Jeffrey Zhong
> Fix For: 0.98.0, 0.95.2
>
>
> This issue happens in distributedLogReplay mode when recovering multiple puts
> of the same key + version(timestamp). After replay, the value is
> nondeterministic of the key
> h5. The original concern situation raised from [~eclark]:
> For all edits the rowkey is the same.
> There's a log with: [ A (ts = 0), B (ts = 0) ]
> Replay the first half of the log.
> A user puts in C (ts = 0)
> Memstore has to flush
> A new Hfile will be created with [ C, A ] and MaxSequenceId = C's seqid.
> Replay the rest of the Log.
> Flush
> The issue will happen in similar situation like Put(key, t=T) in WAL1 and
> Put(key,t=T) in WAL2
> h5. Below is the option I'd like to use:
> a) During replay, we pass wal file name hash in each replay batch and
> original wal sequence id of each edit to the receiving RS
> b) Once a wal is recovered, playing RS send a signal to the receiving RS so
> the receiving RS can flush
> c) In receiving RS, different WAL file of a region sends edits to different
> memstores.(We can visualize this in high level as sending changes to a new
> region object with name(origin region name + wal name hash) and use the
> original sequence Ids.)
> d) writes from normal traffic(allow writes during recovery) are put in normal
> memstores as of today and flush normally with new sequenceIds.
> h5. The other alternative options are listed below for references:
> Option one
> a) disallow writes during recovery
> b) during replay, we pass original wal sequence ids
> c) hold flush till all wals of a recovering region are replayed. Memstore
> should hold because we only recover unflushed wal edits. For edits with same
> key + version, whichever with larger sequence Id wins.
> Option two
> a) During replay, we pass original wal sequence ids
> b) for each wal edit, we store each edit's original sequence id along with
> its key.
> c) during scanning, we use the original sequence id if it's present otherwise
> its store file sequence Id
> d) compaction can just leave put with max sequence id
> Please let me know if you have better ideas.
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