[jira] [Commented] (HBASE-5402) PerformanceEvaluation creates the wrong number of rows in randomWrite

["Jean-Daniel Cryans (Commented) (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HBASE-5402?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13208618#comment-13208618 ] 

Jean-Daniel Cryans commented on HBASE-5402:
-------------------------------------------

I don't see this is an issue, it does create the right amount of rows if you consider counting versions.
                
> PerformanceEvaluation creates the wrong number of rows in randomWrite
> ---------------------------------------------------------------------
>
>                 Key: HBASE-5402
>                 URL: https://issues.apache.org/jira/browse/HBASE-5402
>             Project: HBase
>          Issue Type: Bug
>          Components: test
>            Reporter: Oliver Meyn
>
> The command line 'hbase org.apache.hadoop.hbase.PerformanceEvaluation randomWrite 10' should result in a table with 10 * (1024 * 1024) rows (so 10485760).  Instead what happens is that the randomWrite job reports writing that many rows (exactly) but running rowcounter against the table reveals only e.g 6549899 rows.  A second attempt to build the table produced slightly different results (e.g. 6627689).  I see a similar discrepancy when using 50 instead of 10 clients (~35% smaller than expected).
> Further experimentation reveals that the problem is key collision - by removing the % totalRows in getRandomRow I saw a reduction in collisions (table was ~8M rows instead of 6.6M).  Replacing the random row key with UUIDs instead of Integers solved the problem and produced exactly 10485760 rows.  But that makes the key size 16 bytes instead of the current 10, so I'm not sure that's an acceptable solution.
> Here's the UUID code I used:
>   public static byte[] format(final UUID uuid) {
>     long msb = uuid.getMostSignificantBits();
>     long lsb = uuid.getLeastSignificantBits();
>     byte[] buffer = new byte[16];
>     for (int i = 0; i < 8; i++) {
>       buffer[i] = (byte) (msb >>> 8 * (7 - i));
>     }
>     for (int i = 8; i < 16; i++) {
>       buffer[i] = (byte) (lsb >>> 8 * (7 - i));
>     }
>     return buffer;
>   }
> which is invoked within getRandomRow with 
> return format(UUID.randomUUID());

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