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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-12728) buffered writes substantially less useful after removal of HTablePool
Date Wed, 07 Jan 2015 01:02:52 GMT

    [ https://issues.apache.org/jira/browse/HBASE-12728?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14267096#comment-14267096
] 

stack commented on HBASE-12728:
-------------------------------

Feedback.

On AsyncPutter, will we ever want to buffer Increments or Appends or Deletes (Increments we
might want to aggregate client-side but that is something different from AsyncPutter i suppose);
if so, AsyncMutator instead? (An uglier name!).

Async is probably good to have in the name since it conveys detachment between invocation
and when the op actually happens but on other hand, we could just call it Buffer<Put>
or recast the PutBuffer you have above and do away with an extra moving part?

Ditto, do we even need to expose BufferedTable? Just add to Connection a #getTable(TableName,
PutBuffer) that takes a PutBuffer -- the implementation behind the scenes would use the passed
PutBuffer. I suppose this would mean you'd have to ask Connection for a PutBuffer instance
(Connection#getPutBuffer(maxsize, executor) or maybe this is just where your BufferedConnection
comes in; it adds these methods.

Having the PutBuffer detached from Table is clean but what is to prevent me adding a Put for
TableA to TableB's PutBuffer?  There'd be no protection against this? (That'd probably be
fine)

The flush on BufferedTable is a noop, right?

BufferedTable shouldn't have a close if its not going to do anything?

The ExceptionListener seems good but should it supply more info than just the exception? For
example, where we are in the processing of the buffer -- what edits have succeeded and which
have failed (or would that just be TMI?)

Good stuff [~carterpage]

> buffered writes substantially less useful after removal of HTablePool
> ---------------------------------------------------------------------
>
>                 Key: HBASE-12728
>                 URL: https://issues.apache.org/jira/browse/HBASE-12728
>             Project: HBase
>          Issue Type: Bug
>          Components: hbase
>    Affects Versions: 0.98.0
>            Reporter: Aaron Beppu
>            Assignee: Solomon Duskis
>            Priority: Blocker
>             Fix For: 1.0.0, 2.0.0, 1.1.0
>
>
> In previous versions of HBase, when use of HTablePool was encouraged, HTable instances
were long-lived in that pool, and for that reason, if autoFlush was set to false, the table
instance could accumulate a full buffer of writes before a flush was triggered. Writes from
the client to the cluster could then be substantially larger and less frequent than without
buffering.
> However, when HTablePool was deprecated, the primary justification seems to have been
that creating HTable instances is cheap, so long as the connection and executor service being
passed to it are pre-provided. A use pattern was encouraged where users should create a new
HTable instance for every operation, using an existing connection and executor service, and
then close the table. In this pattern, buffered writes are substantially less useful; writes
are as small and as frequent as they would have been with autoflush=true, except the synchronous
write is moved from the operation itself to the table close call which immediately follows.
> More concretely :
> ```
> // Given these two helpers ...
> private HTableInterface getAutoFlushTable(String tableName) throws IOException {
>   // (autoflush is true by default)
>   return storedConnection.getTable(tableName, executorService);
> }
> private HTableInterface getBufferedTable(String tableName) throws IOException {
>   HTableInterface table = getAutoFlushTable(tableName);
>   table.setAutoFlush(false);
>   return table;
> }
> // it's my contention that these two methods would behave almost identically,
> // except the first will hit a synchronous flush during the put call,
> and the second will
> // flush during the (hidden) close call on table.
> private void writeAutoFlushed(Put somePut) throws IOException {
>   try (HTableInterface table = getAutoFlushTable(tableName)) {
>     table.put(somePut); // will do synchronous flush
>   }
> }
> private void writeBuffered(Put somePut) throws IOException {
>   try (HTableInterface table = getBufferedTable(tableName)) {
>     table.put(somePut);
>   } // auto-close will trigger synchronous flush
> }
> ```
> For buffered writes to actually provide a performance benefit to users, one of two things
must happen:
> - The writeBuffer itself shouldn't live, flush and die with the lifecycle of it's HTableInstance.
If the writeBuffer were managed elsewhere and had a long lifespan, this could cease to be
an issue. However, if the same writeBuffer is appended to by multiple tables, then some additional
concurrency control will be needed around it.
> - Alternatively, there should be some pattern for having long-lived HTable instances.
However, since HTable is not thread-safe, we'd need multiple instances, and a mechanism for
leasing them out safely -- which sure sounds a lot like the old HTablePool to me.
> See discussion on mailing list here : http://mail-archives.apache.org/mod_mbox/hbase-user/201412.mbox/%3CCAPdJLkEzmUQZ_kvD%3D8mrxi4V%3DhCmUp3g9MUZsddD%2Bmon%2BAvNtg%40mail.gmail.com%3E



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