Jason Harvey created CASSANDRA-5099:
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Summary: get_count sometimes returns value smaller than actual
column count
Key: CASSANDRA-5099
URL: https://issues.apache.org/jira/browse/CASSANDRA-5099
Project: Cassandra
Issue Type: Bug
Affects Versions: 1.1.7
Reporter: Jason Harvey
Priority: Minor
We have a CF where keys have thousands of TTLd columns. The columns are
continually added at a regular rate, and TTL out after 15 minutes. We
continually run a 'get_count' on these keys to get a count of the number of
live columns.
Since we upgrade from 1.0 to 1.1.7, "get_count" regularly returns much smaller
values than are possible. For example, with roughly 15,000 columns that have
well-distributed TTLs, running a get_count 10 times will result in 1 or 2
results that are up to half the actual column count. Using a normal 'get' to
count those columns always results in proper values.
For example:
(all of these counts were ran within a second or less of eachother)
{code}
[default@reddit] count AccountsActiveBySR['2qh0u'];
13665 columns
[default@reddit] count AccountsActiveBySR['2qh0u'];
13665 columns
[default@reddit] count AccountsActiveBySR['2qh0u'];
13666 columns
[default@reddit] count AccountsActiveBySR['2qh0u'];
3069 columns
[default@reddit] count AccountsActiveBySR['2qh0u'];
13660 columns
[default@reddit] count AccountsActiveBySR['2qh0u'];
13661 columns
{code}
I should note that this issue happens much more frequently with larger (>10k
columns) keys than smaller keys. It never seems to happen with keys less than
1k columns.
There are no supercolumns in use. The key names and column names are very
short, and there are no column values. The CF is LCS, and due to the TTL only
hovers around a few MB in size.
It appears that there was an issue (CASSANDRA-4833) fixed in 1.1.7 regarding
get_count. Some logic was added to prevent an infinite loop case. Could that
change have resulted in this problem somehow? I can't find any other relevant
1.1 changes that might explain this issue.
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