Re: Add jsonlog log_destination for JSON server logs - Mailing list pgsql-hackers

On Wed, Sep 01, 2021 at 04:39:43PM -0400, Sehrope Sarkuni wrote:
> That makes the elog.c changes in the JSON logging patch minimal as all it's
> really doing is invoking the new write_jsonlog(...) function.

Looking at 0001, to do things in order.

> @@ -46,8 +46,8 @@ typedef struct
>      char        nuls[2];        /* always \0\0 */
>      uint16        len;            /* size of this chunk (counts data only) */
>      int32        pid;            /* writer's pid */
> -    char        is_last;        /* last chunk of message? 't' or 'f' ('T' or
> -                                 * 'F' for CSV case) */
> +    int32        dest;            /* log destination */
> +    char        is_last;        /* last chunk of message? 't' or 'f'*/
>      char        data[FLEXIBLE_ARRAY_MEMBER];    /* data payload starts here */
>  } PipeProtoHeader;

Making PipeProtoHeader larger is not free, and that could penalize
workloads with a lot of short messages and many backends as the
syslogger relies on pipes with sync calls.  Why not switching is_last
to bits8 flags instead?  That should be enough for the addition of
JSON.  3 bits are enough at the end: one to know if it is the last
chunk of message, one for CSV and one for JSON.
--
Michael