Re: patch to allow disable of WAL recycling

Hi,

On 2018-06-26 07:35:57 -0600, Jerry Jelinek wrote:
> +     
> +      wal_recycle (boolean)
> +      
> +       wal_recycle configuration parameter
> +      
> +      
> +      
> +       
> +        When this parameter is on, past log file segments
> +        in the pg_wal directory are recycled for future
> +        use.
> +       
> +
> +       
> +        Turning this parameter off causes past log files segments to be deleted
> +        when no longer needed. This can improve performance by eliminating
> +        read-modify-write operations on old files which are no longer in the
> +        filesystem cache.
> +       
> +      
> +     

This is formulated *WAY* too positive. It'll have dramatic *NEGATIVE*
performance impact of non COW filesystems, and very likely even negative
impacts in a number of COWed scenarios (when there's enough memory to
keep all WAL files in memory).

I still think that fixing this another way would be preferrable. This'll
be too much of a magic knob that depends on the fs, hardware and
workload.

Greetings,

Andres Freund