Re: Measuring the Query Optimizer Effect: Turning off the QO?

On 08/07/2019 01:46, Rob Sargent wrote:
>
>
>> On Jul 7, 2019, at 5:22 PM, Tom Mercha <mercha_t(at)hotmail(dot)com> wrote:
>>
>> Hi All
>>
>> As we know, a query goes through number of stages before it is executed.
>> One of these stages is query optimization (QO).
>>
>> There are various parameters to try and influence optimizer decisions
>> and costs. But I wanted to measure the effect of such a stage by turning
>> it off completely and I can't find such a parameter which explicitly
>> does that. Then I could execute a query to get the effect of "QO active
>> and "QO inactive" and compare.
>>
>> Obviously, I know well what the results would generally look like but I
>> am just interested in measuring the differences for various types of
>> queries. I am also aware that this is a simple comparison - there are
>> more interesting comparisons to perform with QO tweaks, but right now I
>> am interested in something basic.
>>
>> So how would one shut down QO? Or at least, obtaining the guarantee of
>> generating the worst plan possible, ideally without touching many
>> parameters?
>>
>> Best,
>> Tom
>
> Drop all indices?
>

Sorry, maybe my question wasn't clear enough.

A query can be rewritten in various ways by applying rules and costs of
relational algebra operators, as well as their parallelisation. I am
talking about turning off this query optimization, so I am already
assuming that indexes aren't present.