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From "Dag H. Wanvik" <dag.wan...@oracle.com>
Subject Re: is there an optimizer override to force multi-probe query plan?
Date Sat, 27 Jul 2013 22:45:06 GMT
I believe I have seen overrides that specify the  Derby property 
is there are long columns, cf. this code in CreateTableNode (which uses 
properties collected from --DERBY-PROPERIES):

if (table_has_long_column || (approxLength > 
             if (((properties == null) ||
                  (properties.get(Property.PAGE_SIZE_PARAMETER) == null)) &&
                      Property.PAGE_SIZE_PARAMETER) == null))
                 // do not override the user's choice of page size, 
whether it
                 // is set for the whole database or just set on this 

                 if (properties == null)
                     properties = new Properties();


That is, we the user specified a value, use it, else use default. I love 
would for all the possible usages ofr --DERBY-PROPERTIES to ne 
documented in one place...!


On 26/07/13 05:51, Rick Hillegas wrote:
> On 7/25/13 11:39 AM, Rick Hillegas wrote:
>> Hi Mike,
>> This is an attempt to answer your questions based on my recent work 
>> in this code area. Other people may know more than I do.
>> On 7/25/13 8:41 AM, mike matrigali wrote:
>>> Is there an optimizer override in 10.8 to force a multi-probe query 
>>> plan?
>> Not that I'm aware of. Some of the optimizer overrides are documented 
>> in the Tuning Guide section titled "Overriding the default optimizer 
>> behavior". Other overrides are not documented, at least as far as I 
>> can see. The --derby-properties overrides are supposed to be vetted 
>> by the implementations of Optimizable.verifyProperties(). The 
>> following overrides are vetted by these implementations:
>> FromBaseTable.verifyProperties():
>>   index
>>   constraint
>>   joinStrategy
>>   hashInitialCapacity
>>   hashLoadFactor
>>   hashMaxCapacity
>>   bulkFetch
>> FromTable.verifyProperties():
>>   joinStrategy
>>   hashInitialCapacity
>>   hashLoadFactor
>>   hashMaxCapacity
> Here are another two --derby-properties overrides:
> FromList.verifyProperties():
>   joinOrder
>   useStatistics
>>> If not, is there an override in the new work being done in trunk to 
>>> force it?
>> No. The new --derbyplan override merely provides a way to compactly 
>> specify access paths and join strategies.
>>> Also if not, is there any suggestion of what the right syntax would be
>>> to add it to the old style optimizer override?
>> I believe that Bryan and I would prefer to keep the new compact plan 
>> overrides simple. My recommendation would be to use the old-style 
>> --derby-properties for this purpose.
>> If I correctly understand your goal, you are trying to force the use 
>> of a MultiProbeTableScanResultSet. According to DERBY-2503, this 
>> technique is only allowed for NestedLoop joins right now. Maybe the 
>> following new --derby-properties property (handled by FromBaseTable 
>> and FromTable) would capture what you need to specify. This could be 
>> specified anywhere that the index and constraint access paths are 
>> specified. According to the Tuning Guide, that would be at the end of 
>> a table expression:
>> multiProbe=true
>> You may get better advice from people who are more familiar with the 
>> old-style --derby-properties.
>> Hope this helps,
>> -Rick
>>> It seems recently there have been a number of issues where user
>>> expected multi-probe plan but for various reasons the system has
>>> chosen another plan.  Some of these have been bugs, some of these
>>> have been statistics out of date, and most recently the application
>>> would prefer multi-probe for more concurrency even if the execution
>>> is less efficient than full scan.
>>> /mikem

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