[hibernate-dev] Where are the batched fetch statements generated?

Steve Ebersole steve at hibernate.org
Thu Nov 1 15:43:59 EDT 2012

fwiw... I have a lot of this implemented locally.  At the moment it is 
"swappable", but I have not yet exposed this as a setting.  Also, I 
only have (1) and (2) implemented.  (2) is implemented by padding with 
the main identifier that triggered the batch load.

Plan is to work on (3) tomorrow, if I do not get to it today.

https://hibernate.onjira.com/browse/HHH-7746 is the issue I am working 
for this.

On Thu 01 Nov 2012 10:04:03 AM CDT, Steve Ebersole wrote:
> Just to clarify...  (3) is not building the entire statement.  Most of
> the statement can be pre-built.  It just needs to append the proper
> IN-condition
> On Thu 01 Nov 2012 09:30:41 AM CDT, Steve Ebersole wrote:
>> Maybe its best to make this configurable too?
>> I can see 3 selections:
>> 1) current algorithm - the current code as is
>> 2) current size break down but with padding - the current code except
>> selecting the next higher batch size and padding extras (current code
>> selects next smaller size, iteratively)
>> 3) dynamic - dynamically build the batch statement
>> wdyt?
>> On Tue 30 Oct 2012 02:28:31 PM CDT, Steve Ebersole wrote:
>>> Well the other option is to not pre-build/cache the statements for the
>>> batch sizes.  That would free up memory as well as reduce the number
>>> of queries to just one, with the offset being the need to build the
>>> SQL dynamically (although most of it could be built up front).
>>> On 05/08/2012 02:06 AM, Clemens Eisserer wrote:
>>>> Hi Guenther,
>>>>>>> Is it possible to disable prepared statement caching for batched
>>>>>>> fetching, so I end up with a single query in the <
>>>>>>> default_batch_fetch_size case only >>instead of the
>>>>>>> fixed-size batch loading hibernate does by default?
>>>>> I think the main reason for no feedback so far, is that nobody was
>>>>> able to understand this sentence.
>>>>> Usually 'prepared statement caching' is a synonym to 'prepared
>>>>> statement pooling' and is something which has to be provided by a
>>>>> connection-pool (or a jdbc-driver) and thus
>>>>> Hibernate does actually not implement any prepared statement
>>>>> cache/pooling.
>>>>> Can you please explain what you intend under 'prepared statement
>>>>> caching'?
>>>>> Can you also please try to better explain the second part of your
>>>>> sentence?
>>>> Sorry for beeing that cryptic, I will try to rephrase it:
>>>> When Hibernate does batch-fetching, it generates PreparedStatements
>>>> for certain batch sizes - for a batch_size of 50, the prepared
>>>> statements for batch-sizes will have the following sizes:
>>>> [1,2,3,4,5,6,7,8,9,10,12,25,50]. When e.g. a batch of size 13 should
>>>> be fetched, because of the fixed size of the prepared statements, 3
>>>> queries are issued for batch-fetching, although 13 <= 50. In this case
>>>> the 3 batches would be of the size 13 = 8 + 4 + 1.
>>>> In a latency bound (between db and application) environment, this
>>>> serverly hampers response time - instead of a single round-trip to do
>>>> the batched fetch, Hibernate requires 3.
>>>> (subselect can't be used in my case, because my queries are already
>>>> rather complex, and the added complexity confuses the DBs query
>>>> planner too much)
>>>> What I did in this case (only for integer PKs) is to pad up to the
>>>> next batch size with a non-existant PK.
>>>> So, for the example mentioned above, I can use the PreparedStatement
>>>> with size 25, and insert padding from 14-25, which will make the query
>>>> slightly more inefficient but avoid 2 additioan round-trips.
>>>> - Clemens
>>>> _______________________________________________
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>> --
>> steve at hibernate.org
>> http://hibernate.org
> --
> steve at hibernate.org
> http://hibernate.org

steve at hibernate.org

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