Re: need suggestion on querying big tables

On 12/5/22 01:35, Holger Jakobs wrote:
> Am 05.12.22 um 07:29 schrieb Ebin Jozer:
>> Hi Team,
>> in postgresql 11 version we have two tables of size 435 GB and 347 GB.
>> if we query on single table or if we are doing inner join on both the big
>> tables, it is not displacing any output, it keeps running
>>
>> We can see the wait event is IO and directDatafile .
>>
>> Server Spec : 8 cores and  64GB RAM
>> PG config : 53 GB(effective_cache), 12 GB(shared buffer)
>>
>> can you please suggest some ideas , how we can query on big tables and
>> fasten them to get the output??
>>
>> Thanks & Regards,
>> /Ebin/
>
> There are basically two "secrets" to performance in this case:
>
> 1. make sure that the join operation uses indexes
> 2. make sure that you have enough work_mem available
>
> work_mem can be set in postgresql.conf, but also in every session
> individually. So don't set it too high generally, because it will be
> allocated for every sorting and hashing operation.
>

A "just smart enough" user could perform an inadvertent Denial of Service
attack on the database by cranking his session work_mem really high, no?

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