Re: Very slow 101-feeling design/query..

Keep in mind that using UUIDs as an ID on large data sets will use double the memory and index size.  Obviously, if that is set in stone, you probably can't readily change it, but I'd think twice before using that for billions of rows for joining.

Sent from my iPhone

On Dec 11, 2021, at 2:38 PM, Wells Oliver <wells.oliver@gmail.com> wrote:



Yeah, I can take a look at that. The other issue is simply doing SELECT * FROM vw_joints WHERE game_id = 123 is slow because joints -> plays on play_uuid, and the index is on game_id in plays, but that query is slower than I want it to be.

On Sat, Dec 11, 2021 at 11:22 AM Mladen Gogala <gogala.mladen@gmail.com> wrote:

On 12/11/21 13:32, Wells Oliver wrote:

We have hundreds of millions of joint locations across hundreds of thousands of plays across thousands of games. We also have a few hundred games with plays in them, but no joint measurements. The joint data is a measurement of body joints through time (up to 300x a second)

So my idea was the plays table contains the game identifier (there is no root game table), and the joints table refers to the plays table by a play UUID.

As an example: One game contains 231 plays. There are 396,144 rows of joint data.

I partitioned the joints data by month because of the volume.

The end result is using the joints view (which joins to plays) is just dead, grinding slow, and I'm trying to think of alternatives that stay within Postgres, i.e. maybe BigQuery and/or RedShift is more of an appropriate solution, but I don't want to go there quite yet.

Just trying to optimize this design and open to ideas. Thanks.

On Sat, Dec 11, 2021 at 7:58 AM Michel SALAIS <msalais@msym.fr> wrote:

Hi

Using view which does a join in two tables to access things in one of them is not a good idea. You pay for a join even though it is not necessary. So if you just want distinct game_id and you don’t care if its play_uuid is in joints, then you can accelerate using the table plays directly.

 

Michel SALAIS

De : Wells Oliver <wells.oliver@gmail.com>
Envoyé : vendredi 10 décembre 2021 23:53
À : pgsql-admin <pgsql-admin@postgresql.org>
Objet : Very slow 101-feeling design/query..

 

This feels very 101 but I feel like it should be much faster:

 

A table "joints" with a PK of play_uuid, target_id, joint_seq, joint_timestamp.

 

"joints" is partitioned using RANGE on joint_timestamp for monthly partitions 1/1 - 2/1, 2-1 - 3/1, etc.

 

"joints" has an FK where play_uuid refers to table "plays" and column "play_uuid" where "play_uuid" is the PK.

 

"plays" additionally has an indexed column game_id.

 

"joints" has 1133,932,391 rows across 12 monthly partitions for 2021, and "plays has 585,627 rows. We made a view called "vw_joints" which just does:

 

SELECT * FROM joints JOIN plays USING (play_id);

 

Then doing:

 

SELECT DISTINCT game_id FROM vw_joints

 

Takes 35-45 minutes. Which seems nuts. We do this kind of design in a few different plays to normalize things, but it comes at the cost of these agonizingly slow (and seemingly dead simple) qeuries.

 

Is there any optimization to do here beyond flattening table and de-normalizing data? Is the partitioning causing a slowness here? I feel like partitioning is creating some difficulty...

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Well, you can create a trigger which would fire whenever row is inserted or deleted and would update joint, game_id and the count in a separate table. That is the usual solution for the problem you described. Also, if there is a small amount of games, you can use hash index instead of B-tree indexes.

--

Mladen Gogala
Database Consultant
Tel: (347) 321-1217
https://dbwhisperer.wordpress.com

--

Wells Oliver
wells.oliver@gmail.com