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From "ryan rawson (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-2939) Allow Client-Side Connection Pooling
Date Tue, 01 Mar 2011 01:49:37 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2939?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13000661#comment-13000661
] 

ryan rawson commented on HBASE-2939:
------------------------------------

I ran this on a little cluster test and my results were a little mixed.  This is due to my
set up and my benchmarking setup.

- using YCSB and a small working set I loaded data on Regionserver R1
- ran YCSB with small 300 row scans with 100 columns on Master M
- ran with both this patch, and without.

The test runs with this patch did not indicate significant improvement.  I think this was
due to the fact that I was saturating the network between M and R1, and opening more sockets
gave slight but not significant improvement.  I didn't capture the numbers, but it was something
like 390 ms without and 340 ms with.

I ran in a fairly interesting case since I was trying to test the contention of the single
socket, and it seems like adding more sockets to a saturated network did not improve like
I had hoped to.

Could you paste in your test scenario?  I could see that for some scenarios involving small
to medium gets, that this could provide an improvement to latency.

> Allow Client-Side Connection Pooling
> ------------------------------------
>
>                 Key: HBASE-2939
>                 URL: https://issues.apache.org/jira/browse/HBASE-2939
>             Project: HBase
>          Issue Type: Improvement
>          Components: client
>    Affects Versions: 0.89.20100621
>            Reporter: Karthick Sankarachary
>            Assignee: ryan rawson
>            Priority: Critical
>             Fix For: 0.92.0
>
>         Attachments: HBASE-2939-0.20.6.patch, HBASE-2939.patch, HBASE-2939.patch
>
>
> By design, the HBase RPC client multiplexes calls to a given region server (or the master
for that matter) over a single socket, access to which is managed by a connection thread defined
in the HBaseClient class. While this approach may suffice for most cases, it tends to break
down in the context of a real-time, multi-threaded server, where latencies need to be lower
and throughputs higher. 
> In brief, the problem is that we dedicate one thread to handle all client-side reads
and writes for a given server, which in turn forces them to share the same socket. As load
increases, this is bound to serialize calls on the client-side. In particular, when the rate
at which calls are submitted to the connection thread is greater than that at which the server
responds, then some of those calls will inevitably end up sitting idle, just waiting their
turn to go over the wire.
> In general, sharing sockets across multiple client threads is a good idea, but limiting
the number of such sockets to one may be overly restrictive for certain cases. Here, we propose
a way of defining multiple sockets per server endpoint, access to which may be managed through
either a load-balancing or thread-local pool. To that end, we define the notion of a SharedMap,
which maps a key to a resource pool, and supports both of those pool types. Specifically,
we will apply that map in the HBaseClient, to associate multiple connection threads with each
server endpoint (denoted by a connection id). 
>  Currently, the SharedMap supports the following types of pools:
>     * A ThreadLocalPool, which represents a pool that builds on the ThreadLocal class.
It essentially binds the resource to the thread from which it is accessed.
>     * A ReusablePool, which represents a pool that builds on the LinkedList class. It
essentially allows resources to be checked out, at which point it is (temporarily) removed
from the pool. When the resource is no longer required, it should be returned to the pool
in order to be reused.
>     * A RoundRobinPool, which represents a pool that stores its resources in an ArrayList.
It load-balances access to its resources by returning a different resource every time a given
key is looked up.
> To control the type and size of the connection pools, we give the user a couple of parameters
(viz. "hbase.client.ipc.pool.type" and "hbase.client.ipc.pool.size"). In case the size of
the pool is set to a non-zero positive number, that is used to cap the number of resources
that a pool may contain for any given key. A size of Integer#MAX_VALUE is interpreted to mean
an unbounded pool.

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