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https://issues.apache.org/jira/browse/HBASE-12728?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14266961#comment-14266961
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Enis Soztutar commented on HBASE-12728:
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I think API wise, what Carter proposes above makes sense with a couple of
comments.
- I think {{BufferedTable}} should be an interface still with {{flush()}} or
{{flushCommits()}} method.
- {{ExceptionListener}} should also get the original {{Put}} so that it can
learn about which operation has failed (not just the exception).
- Do we want AsyncPutter, etc to be client-public API at all? I like the
{{BufferedConnection}} route where we can have getBufferedTable() method to
construct this and not worry about any class. However do we want to address
doing puts() with flush and doing async flush by the same client? Does the
client maintain two Connection objects?
- Should the interfaces be {{Put}} based or {{Mutation}} based? We can make it
generic in case of we add Delete's later on, but may not be worth the extra
cost.
bq. BufferedTable#close does not flush since we need to support batching across
multiple threads. AsyncPutter#close does flush.
Seems a bit unintuitive. If we do the BufferedConnection route, the only way to
flush everything is to
bq. Do we need a timeout-based flush?
It makes sense, but this can be added later I say.
> 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
> 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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