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From "Jason Bray (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-8762) Performance/operational penalty when calling HTable.get with a list of one Get
Date Tue, 18 Jun 2013 21:30:20 GMT
Jason Bray created HBASE-8762:
---------------------------------

             Summary: Performance/operational penalty when calling HTable.get with a list
of one Get
                 Key: HBASE-8762
                 URL: https://issues.apache.org/jira/browse/HBASE-8762
             Project: HBase
          Issue Type: Bug
          Components: Client
            Reporter: Jason Bray
            Priority: Minor


There are two implications to calling HTable.get with a list of one Get.
1. The overhead of processBatch is paid unnecessarily, which is not insignificant.
2. The get requests show up as a 'multi' when reviewing RPC handlers, when the request should
just be a single Get.  It seems likely that there are other places in logs/ui it shows up
as a multi as well.

To give some context to the overhead, here are some timings performed by a member of our team:

In a very simple test, of reading the same key 100 times, taking the time it took, and then
repeating this 10 times (1000 total gets), the times are as follows (excluding the actual
first iteration as there was considerable HBase warm-up times on the JVM for establishing
connections):
||Iteration||Batch (in ms)||Single (in ms)||
|1|2255|815| 
|2|1545|823| 
|3|1427|742| 
|4|1451|721| 
|5|1480|775| 
|6|1379|735| 
|7|1657|775| 
|8|1392|804|

While I can see the argument that callers should use the single Get method signature, the
cost implications are somewhat surprising and it's very easy to be smart in this case.  We
simply need to have HTable.get(List<Get>) delegate to HTable.get(<Get>) if the
list has one Get.

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