Re: Blocked updates and background writer performance

Maybe you're not doing this.... but:
Using "data" json(b)/hstore column for all/most/many fields is an
antipattern. Use 'data' *ONLY* for columns that you know will be dynamic.
This way you'll write less data into static-columns (no key-names overhead
and better types) --> less data to disk etc (selects will also be faster).

On Tue, Jan 12, 2016 at 7:25 PM, Cory Tucker <cory(dot)tucker(at)gmail(dot)com> wrote:

> PG 9.4.4 (RDS)
>
> I'm experiencing an issue when trying to update many rows in a single
> table (one row at a time, but parallelized across ~12 connections). The
> issue we see is that the writes will periodically be blocked for a duration
> of several minutes and then pick back up. After digging through our
> monitoring stack, I was able to uncover these stats which seem to allude to
> it being a background writer performance problem:
>
> [image: bg_writer.png]
> (apologies for the image)
>
> Our settings for the background writer are pretty standard OOB (I threw in
> some others that I thought might be helpful, too):
>
> name | setting | unit
> -------------------------+---------+------
> bgwriter_delay | 200 | ms
> bgwriter_lru_maxpages | 100 |
> bgwriter_lru_multiplier | 2 |
> maintenance_work_mem | 65536 | kB
> max_worker_processes | 8 |
> work_mem | 32768 | kB
>
>
> The table that is being written to contains a jsonb column with a GIN
> index:
>
> Table "public.ced"
> Column | Type | Modifiers
> ---------------+--------------------------+-----------
> id | bigint | not null
> created_at | timestamp with time zone |
> modified_at | timestamp with time zone |
> bean_version | bigint | default 0
> account_id | bigint | not null
> data | jsonb | not null
> Indexes:
> "ced_pkey" PRIMARY KEY, btree (id)
> "ced_data" gin (data jsonb_path_ops)
> "partition_key_idx" btree (account_id, id)
>
>
> It seems to me that the background writer just can't keep up with the
> amount of writes that I am trying to do and freezes all the updates. What
> are my options to improve the background writer performance here?
>
> thanks
> --Cory
>
>
>