Re: Query Performance / Planner estimate off

вт, 20 окт. 2020 г. в 16:50, Mats Olsen <mats(at)duneanalytics(dot)com>:

> On 10/20/20 3:04 PM, Victor Yegorov wrote:
>
> вт, 20 окт. 2020 г. в 11:38, Mats Julian Olsen <mats(at)duneanalytics(dot)com>:
>
>> I'm looking for some help to manage queries against two large tables.
>>
>
> Can you tell the version you're running currently and the output of this
> query, please?
>
> select name,setting,source from pg_settings where source not in
> ('default','override');
>
> Running "PostgreSQL 12.2 (Ubuntu 12.2-2.pgdg19.10+1) on
> x86_64-pc-linux-gnu, compiled by gcc (Ubuntu 9.2.1-9ubuntu2) 9.2.1
> 20191008, 64-bit"
>
> Updated the gist to include the results forom pg_settings. Here's the
> direct link
> https://gist.githubusercontent.com/mewwts/9f11ae5e6a5951593b8999559f5418cf/raw/e5deebbbb48680e04570bec4e9a816fa009da34f/pg_settings
>
It looks like indexes currently chosen by the planner don't quite fit your
query.

I would create the following index (if it's possible to update schema):
ON "uniswap_v2.Pair_evt_Mint" (evt_tx_hash, evt_block_time)

Same for the second table, looks like
ON "ethereum.transactions" (hash, block_time)
is a better fit for your query. In fact, I do not think
`transactions_block_number_time` index is used frequently, 'cos second
column of the index is a partitioning key.

Currently planner wants to go via indexes 'cos you've made random access
really cheap compared to sequential one (and your findings shows this).
Perhaps on a NVMe disks this could work, but in your case you need to find
the real bottleneck (therefore I asked for buffers).

I would set `random_page_cost` to a 2.5 at least with your numbers. Also, I
would check DB and indexes for bloat (just a guess now, 'cos your plans
miss buffers figures).

--
Victor Yegorov