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https://issues.apache.org/jira/browse/HBASE-12728?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14278781#comment-14278781
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Solomon Duskis commented on HBASE-12728:
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bq. Yes. But HTable is going underground, right? And Table is what users are
left with? HTable constructors are deprecated. It is becoming an internalized
implementation. Whats a fella who wants to do buffering or "short-lived-ness"
to do going forward?
In terms of buffering, why not simply keep autoflush and suggest
synchronization on a Table in a multi-threaded environment? That would solve
the user's original issue.
In all of this discussion, it feels like there isn't consensus about separating
Table from BM functionality. Some want to remove Table.autoflush and some want
to keep it. I don't have a strong view either way at this point. I'll be glad
to continue to help, but I don't want to invest too much more time in
implementation details until a consensus exists for a more coherent strategy.
If BM is a Good Thing (tm) because it's a coherent unit and HT (and maybe Table
even) is amorphous legacy, then perhaps it's more worthwhile taking a look at
segmenting Table as a whole into coherent units rather than focusing on BM
alone.
> 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
> Priority: Blocker
> Fix For: 1.0.0, 2.0.0, 1.1.0
>
> Attachments: 12728.connection-owns-buffers.example.branch-1.0.patch,
> HBASE-12728-2.patch, HBASE-12728.patch, bulk-mutator.patch
>
>
> 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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