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From "Thakrar, Jayesh" <jthak...@conversantmedia.com>
Subject Re: Cassandra crashes....
Date Wed, 23 Aug 2017 05:25:53 GMT
So the reason for the large number of prepared statements is because of the nature of the application.
One of the periodic job does lookup with a partial key (key prefix, not filtered queries)
for thousands of rows.
Hence the large number of prepared statements.

Almost of the queries once executed are not needed anymore, so its ok for the older prepared
statements to be purged.

All the same, I will do some analysis on the prepared statements table.

Thanks for the tip/pointer!

On 8/22/17, 5:17 PM, "Alain Rastoul" <alf.mmm.cat@gmail.com> wrote:

    On 08/22/2017 05:39 PM, Thakrar, Jayesh wrote:
    > Surbhi and Fay,
    >
    > I agree we have plenty of RAM to spare.
    >
    
    Hi
    
    At the very beginning of system.log there is a
    INFO  [CompactionExecutor:487] 2017-08-21 23:21:01,684 
    NoSpamLogger.java:91 - Maximum memory usage reached (512.000MiB), cannot 
    allocate chunk of 1.000MiB
    who comes from BufferPool exhaustion (several messages)
     From the source&doc
    file_cache_size_in_mb
         (Default: Smaller of 1/4 heap or 512) Total memory to use for 
    SSTable-reading buffers.
    
    So here in your configuration it is 512M, may be you should set it to a 
    higher value in your cassandra.yaml (1/4 => 4G) ?
    (also see https://issues.apache.org/jira/browse/CASSANDRA-11681, the 
    default value may not be accurate)
    
    Another strange thing is the number of prepared statements which also 
    gives errors: lot of messages like
    WARN  [ScheduledTasks:1] 2017-08-22 07:09:25,009 QueryProcessor.java:105 
    - 1 prepared statements discarded in the last minute because cache limit 
    reached (64 MB)
    ...
    on startup you see:
    INFO  [main] 2017-08-22 12:50:13,787 QueryProcessor.java:162 - Preloaded 
    13357 prepared statements
    
    13K different prepared statements sounds a lot...
    an issue about that seems to be fixed in 3.11 
    https://issues.apache.org/jira/browse/CASSANDRA-13641
    May be youc should truncate your system.prepared_statements and restart 
    your node
    
    
    HTH
    
    
    -- 
    best,
    Alain
    
    


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