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From Stuart Broad <stu...@moogsoft.com>
Subject Re: Prepared Statement - cache duration (CQL3 - Cassandra 1.2.4)
Date Tue, 23 Apr 2013 15:13:47 GMT
Hi Edward,

Thanks for your reply - I was already using the prepare/execute cql methods
that you suggested.  My problem is that these methods 'mask' the
PreparedQueryNotFoundException as an InvalidRequestException.  At present I
catch the InvalidRequestException (when cassandra has been re-started) and
check the message text to figure out if I need to rebuild the prepared
queries (rather than building each time I call).

Sylvain had suggested that I use the binary protocol as the exceptions are
more explicit so I am trying to determine how this can be done (I don't see
any obvious methods other than the cql ones for calling prepared
statements).

Regards,

Stuart


On Tue, Apr 23, 2013 at 4:05 PM, Edward Capriolo <edlinuxguru@gmail.com>wrote:

> Thrift has a prepare_cql call which returns an ID. Then it has an
> exececute_cql call which takes the id and a map or variable bindings.
>
>
> On Tue, Apr 23, 2013 at 10:29 AM, Stuart Broad <stuart@moogsoft.com>wrote:
>
>> Hi all,
>>
>> I just realised that the binary protocol is the low-level thrift api that
>> I was originally using (Cassandra.Client>> get / insert ...).  How can a
>> prepared statement be called through the thrift api (i.e. not the cql
>> methods)?
>>
>> Cheers,
>>
>> Stuart
>>
>>
>> On Tue, Apr 23, 2013 at 11:48 AM, Stuart Broad <stuart@moogsoft.com>wrote:
>>
>>> Hi Sylvain,
>>>
>>> Thanks for your response.  I am handling the
>>> 'PreparedQueryNotFoundException' more for the case of a cassandra re-start
>>> (rather then expecting to build 100000 statements).
>>>
>>> I am not familiar with the binary protocol - which class/methods should
>>> I look at?
>>>
>>> Regards,
>>>
>>> Stuart
>>>
>>>
>>>
>>> On Tue, Apr 23, 2013 at 11:29 AM, Sylvain Lebresne <sylvain@datastax.com
>>> > wrote:
>>>
>>>> In thrift, a lot of exceptions (like PreparedQueryNotFoundException)
>>>> are simply returned as InvalidRequestException. The reason for that was a
>>>> mix of not wanting to change the thrift API too much and because we didn't
>>>> knew how to return a lot of different exception with thrift without making
>>>> it horrible to work with. So you'll probably have to parse strings here
>>>> indeed.
>>>>
>>>> This will be cleaner/less fragile if you use the binary protocol as
>>>> exceptions are more fined grained there.
>>>>
>>>> Though taking a step back (and without saying that you shouldn't handle
>>>> the case where a query is not prepared on the node you contact), if you're
>>>> really considering preparing more than 100000 statements, I'd suggest that
>>>> it might be worth benchmarking whether using prepared statements in your
>>>> case is really going to be worth the trouble. Just saying.
>>>>
>>>> --
>>>> Sylvain
>>>>
>>>>
>>>>
>>>> On Tue, Apr 23, 2013 at 12:14 PM, Stuart Broad <stuart@moogsoft.com>wrote:
>>>>
>>>>> Hi Sorin,
>>>>>
>>>>> The PreparedQueryNotFoundException is not thrown from
>>>>> Cassandra.Client>>execute_prepared_cql3_query method.  I created
some
>>>>> prepared statements and then re-started cassandra and received the
>>>>> following exception:
>>>>>
>>>>> InvalidRequestException(why: Prepared query with ID 1124421588 not
>>>>> found (either the query was not prepared on this host (maybe the host
has
>>>>> been restarted?) or you have prepared more than 100000 queries and queries
>>>>> 1124421588 has been evicted from the internal cache))
>>>>>
>>>>> The best I have been able to come up with is the following:
>>>>>
>>>>>             try {
>>>>>                 client.execute_prepared_cql3_query(psId, bindValues,
>>>>> ..);
>>>>>             } catch (InvalidRequestException invEx) {
>>>>>                 String why = invEx.getWhy();
>>>>>                 CLogger.logger().warning(why);
>>>>>                 if(why.startsWith("Prepared query with ID")) {
>>>>>                     rebuildPreparedStatement(preparedStatement);
>>>>>                     client.execute_prepared_cql3_query(psId,
>>>>> bindValues, ..);
>>>>>                 } else {
>>>>>                     throw invEx;
>>>>>                 }
>>>>>             }
>>>>>
>>>>> Obviously this is pretty fragile and would break if the cassandra
>>>>> message was changed...but it least it works for now!
>>>>>
>>>>> Cheers,
>>>>>
>>>>> Stuart
>>>>>
>>>>>
>>>>> On Sun, Apr 21, 2013 at 11:51 AM, Sorin Manolache <sorinm@gmail.com>wrote:
>>>>>
>>>>>> On 2013-04-19 13:57, Stuart Broad wrote:
>>>>>>
>>>>>>> Hi,
>>>>>>>
>>>>>>> I am using Cassandra.Client
>>>>>>> prepare_cql3_query/execute_**prepared_cql3_query to create and
run
>>>>>>> some
>>>>>>> prepared statements.  It is working well but I am unclear as
to how
>>>>>>> long
>>>>>>> the server side 'caches' the prepared statements.  Should a prepared
>>>>>>> statement be prepared for every new Cassandra.Client?  Based
on my
>>>>>>> limited testing it seems like I can create some prepared statements
>>>>>>> in
>>>>>>> one Cassandra.Client and use in another but I am not sure how
>>>>>>> reliable/lasting this is i.e.  If I called the prepared statement
>>>>>>> again
>>>>>>> the next day would it still exist?  What about if cassandra was
>>>>>>> re-started?
>>>>>>>
>>>>>>> _Background:_
>>>>>>>
>>>>>>> I am creating prepared statements for batch updates of pre-defined
>>>>>>> lengths (e.g. 10000, 1000, 500, 250, 50, 10, 1) and wanted to
know if
>>>>>>> these could just be set up once.  We felt that using the prepared
>>>>>>> statements was easier than escaping values within a CQL statement
and
>>>>>>> probably more performant.
>>>>>>>
>>>>>>> Thanks in advance for your help.
>>>>>>>
>>>>>>>
>>>>>> I've looked in Cassandra's code (v1.2.3). The cache of prepared
>>>>>> statements has a size of 100,000. So if you prepare more than 100
thousand
>>>>>> statements, the least recently used ones will vanish. You'll get
the
>>>>>> exception PreparedQueryNotFoundException**, code 0x2500.
>>>>>>
>>>>>> Regards,
>>>>>> Sorin
>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>

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