Increasing max_wal_size

[Mike Hardy]

Hiya, we're using Postgres on Cloud SQL and our logs continuously show us two messages.

LOG:  checkpoints are occurring too frequently (15 seconds apart) 
HINT:  Consider increasing the configuration parameter "max_wal_size". 

However, I see on the supported flags documentation that this flag is not supported by Cloud SQL. Is there anything we can do about this?

Cheers,
Mike

[Kenworth (Google Cloud Platform)]

Per this Postgres WAL (Write Ahead Log) docs, The default size is 1 GB and you can set this parameter in the postgresql.conf file or on the server command line.

[Mike Hardy]

Kenworth,thanks but I don't think Cloud SQL users can edit postgresql.conf, can we? If it is possible, please share the documentation.

[Vladimir Rusinov]

Hi Mike,

You are right - we don't provide a way to edit postgresql.conf directly, and max_wal_size is not one of parameters we expose through flags. It is also unlikely that we will start exposing it in near future.

However, we set it to 1.5G on most of the instances. We did some preliminary testing and found out that  on our infrastructure higher values provide diminishing returns while increasing crash recovery times. So we felt 1.5G is a good trade-off between performance and MTTR in case of a failure.

We may of course revisit this decision in the future. Please open a feature request if you feel like this is limiting performance for your workload.

Thank you for using our service!

--
Vladimir Rusinov
PostgreSQL SRE, Google Ireland

Google Ireland Ltd.,Gordon House, Barrow Street, Dublin 4, Ireland
Registered in Dublin, Ireland
Registration Number: 368047

On Sun, Oct 29, 2017 at 10:00 PM, Mike Hardy <mha...@localinsights.io> wrote:

Kenworth,thanks but I don't think Cloud SQL users can edit postgresql.conf, can we? If it is possible, please share the documentation.

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