From: MichaelDBA <MichaelDBA@sqlexec.com>
To: Wells Oliver <wells.oliver@gmail.com>
Cc: pgsql-admin <pgsql-admin@postgresql.org>
Subject: Re: Declarative partitioning, UUIDs, index issues.
Date: Mon, 13 Jan 2020 15:41:00 -0500
Message-ID: <96ab1ca0-c527-8ba9-dedc-5cfe90eecc1e@sqlexec.com> (raw)
In-Reply-To: <CAOC+FBXcPFFF=e=OUYnPSZc+_6j=TTAMFceQhKRPUjJR9dmvgQ@mail.gmail.com>
References: <CAOC+FBXcPFFF=e=OUYnPSZc+_6j=TTAMFceQhKRPUjJR9dmvgQ@mail.gmail.com>
Hi Oliver,
I know I am not addressing your immediate concern about why it is not
using the index, but I have another question first:
You are using a query that is not doing any partition exclusion since
you are not providing the date on the where clause, which is the
partitioning key, right? If so, I would expect to see all the
partitions in the explain output, but I only see 4 thru 8.
Regards,
Michael Vitale
Wells Oliver wrote on 1/13/2020 12:21 PM:
> Hi all. I have a table with 7 columns: uuid, date, smallint, smallint,
> real, real, real.
>
> The PK is the uuid, date, smallint, smallint.
>
> It has 60 partitions on date, partitioned by month, back to 2015. Each
> partition is roughly 40GB, about 350-450m rows.
>
> Doing a join to this table using the uuid is not using an index, so
> it's never completing. So where this table is b: SELECT * FROM a JOIN
> b ON A.uuid = B.uuid - I thought it might use the PK as the uuid is
> the first column, but we end up with a ton of sequence scans:
>
> Hash Join (cost=113773.34..326420199.08 rows=1187847 width=46)
> Hash Cond: (a.uuid = myt.uuid)
> -> Append (cost=0.00..282743385.62 rows=11613643108 width=42)
> -> Seq Scan on myt_2015_05 myt_4 (cost=0.00..7647300.32
> rows=395295232 width=42)
> -> Seq Scan on myt_2015_06 myt_5 (cost=0.00..7233480.44
> rows=373904544 width=42)
> -> Seq Scan on myt_2015_07 myt_6 (cost=0.00..6679997.60
> rows=345294560 width=42)
> -> Seq Scan on myt_2015_08 myt_7 (cost=0.00..7426294.64
> rows=383871264 width=42)
> -> Seq Scan on myt_2015_09 myt_8 (cost=0.00..7454691.04
> rows=385339104 width=42)
>
> Etc, all the way up to present. I then tried adding a btree index on
> the uuid itself, same result.
>
> Selecting directly on the table where the uuid = some value will use
> the index, but joining to the table will NOT.
>
> I ran analyze on the primary table, still a sequence scan.
>
> This table is useless without an index on the uuid, what might be the
> issue? Might my partitions be too large? Something else?
>
> --
> Wells Oliver
> wells.oliver@gmail.com <mailto:wellsoliver@gmail.com>
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To: pgsql-admin@postgresql.org
Cc: MichaelDBA@sqlexec.com, wells.oliver@gmail.com
Subject: Re: Declarative partitioning, UUIDs, index issues.
In-Reply-To: <96ab1ca0-c527-8ba9-dedc-5cfe90eecc1e@sqlexec.com>
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