In the absence of a num_versions qualifier, shell makes presumption that
you want ALL versions. Changing the default to be 1 would mean that we
would have to add some other means of specifying all versions
("num_versions=-1" or some such oddity). What ye think?
St.Ack
Jim Kellerman wrote:
Yes, for num_versions > 1, HBase has to dig through the memcache, and multiple
HStore files until it has found the requested number of versions or runs out of
places to look. This is especially apparent if there is only 1 version. It has to
do a lot of work for nothing.
Please enter a Jira for the HBase shell to default the number of versions to 1.
---
Jim Kellerman, Senior Engineer; Powerset
[EMAIL PROTECTED]
-----Original Message-----
From: Stu Hood [mailto:[EMAIL PROTECTED]
Sent: Tuesday, November 06, 2007 11:23 PM
To: [email protected]
Subject: HBase num_versions
Hey guys,
Just noticed some surprising behavior for select statements
in HBase 0.15: a select command without a num_versions = 1
clause takes 2 orders of magnitude longer to run than a bare select.
Is this inconsistent implementation, or is it taking extra
time to scan for additional versions? If this isn't a bug,
then perhaps the default for num_versions should be 1 to keep
things snappy by default.
============================================================
Hbase> describe test;
+-------------------------------------------------------------
----------------+
| Column Family Descriptor
|
+-------------------------------------------------------------
----------------+
| name: hex, max versions: 3, compression: NONE, in memory:
false, max length:|
| 2147483647, bloom filter: none
|
+-------------------------------------------------------------
----------------+
1 columnfamily(s) in set (0.310 sec)
Hbase> select hex: from test where row = '3980000' num_versions = 1;
3cbae0
1 row(s) in set (0.016 sec)
Hbase> select hex: from test where row = '3980000';
3cbae0
1 row(s) in set (1.882 sec)
============================================================
Thanks,
Stu Hood
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