Re: Fdw batch insert error out when set batch_size > 65535

On 6/9/21 12:22 PM, Tomas Vondra wrote:
> 
> 
> On 6/9/21 8:28 AM, Tom Lane wrote:
>> I wrote:
>>> Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com> writes:
>>>>> I've added a simple regression test to postgres_fdw, testing that 
>>>>> batch
>>>>> sizes > 65535 work fine, and pushed the fix.
>>
>>>> I was earlier thinking of adding one, but stopped because it might
>>>> increase the regression test execution time. It looks like that's true
>>>> - with and without the test case it takes 17 sec and 4 sec
>>>> respectively on my dev system which is 4X slower. I'm not sure if this
>>>> is okay.
>>
>>> The cost, versus the odds of ever detecting a problem, doesn't
>>> seem like a good tradeoff.
>>
>> I took a quick look and noted that on buildfarm member longfin
>> (to take a random example that's sitting a few feet from me),
>> the time for contrib-install-check went from 34 seconds before
>> this patch to 40 seconds after.  I find that completely
>> unacceptable compared to the likely value of this test case.
>>
> 
> Note that the problem here is [1] - we're creating a lot of slots 
> referencing the same tuple descriptor, which inflates the duration. 
> There's a fix in the other thread, which eliminates ~99% of the 
> overhead. I plan to push that fix soon (a day or two).
> 

Forgot to add the link:

[1] 
https://www.postgresql.org/message-id/ebbbcc7d-4286-8c28-0272-61b4753af761%40enterprisedb.com


regards

-- 
Tomas Vondra
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