Re: pg_walinspect - a new extension to get raw WAL data and WAL stats

On Fri, Mar 11, 2022 at 7:53 PM Ashutosh Sharma <ashu(dot)coek88(at)gmail(dot)com> wrote:
>
> Some comments on pg_walinspect-docc.patch this time:
>
> + <varlistentry>
> + <term>
> + <function>pg_get_wal_record_info(in_lsn pg_lsn, lsn OUT pg_lsn,
> prev_lsn OUT pg_lsn, xid OUT xid, resource_manager OUT text, length
> OUT int4, total_length OUT int4, description OUT text, block_ref OUT
> text, data OUT bytea, data_len OUT int4)</function>
> + </term>
>
> You may shorten this by mentioning just the function input parameters
> and specify "returns record" like shown below. So no need to specify
> all the OUT params.
>
> pg_get_wal_record_info(in_lsn pg_lsn) returns record.
>
> Please check the documentation for other functions for reference.
>
> ==
>
> + <term>
> + <function>pg_get_wal_records_info(start_lsn pg_lsn, end_lsn
> pg_lsn DEFAULT NULL, lsn OUT pg_lsn, prev_lsn OUT pg_lsn, xid OUT xid,
> resource_manager OUT text, length OUT int4, total_length OUT int4,
> description OUT text, block_ref OUT text, data OUT bytea, data_len OUT
> int4)</function>
> + </term>
>
> Same comment applies here as well. In the return type you can just
> mention - "returns setof record" like shown below:
>
> pg_get_wal_records_info(start_lsn pg_lsn, end_lsn pg_lsn) returns setof records.
>
> You may also check for such optimizations at other places. I might
> have missed some.

I used the way verify_heapam shows the columns as it looks good IMO
and we can't show sample outputs for all of the functions in the
documentation.

> ==
>
> +<screen>
> +postgres=# select prev_lsn, xid, resource_manager, length,
> total_length, block_ref from pg_get_wal_records_info('0/158A7F0',
> '0/1591400');
> + prev_lsn | xid | resource_manager | length | total_length |
> block_ref
> +-----------+-----+------------------+--------+--------------+--------------------------------------------------------------------------
> + 0/158A7B8 | 735 | Heap | 54 | 7838 | blkref
> #0: rel 1663/5/2619 blk 18 (FPW); hole: offset: 88, length: 408
> + 0/158A7F0 | 735 | Btree | 53 | 8133 | blkref
> #0: rel 1663/5/2696 blk 1 (FPW); hole: offset: 1632, length: 112
> + 0/158C6A8 | 735 | Heap | 53 | 873 | blkref
> #0: rel 1663/5/1259 blk 0 (FPW); hole: offset: 212, length: 7372
>
> Instead of specifying column names in the targetlist I think it's
> better to use "*" so that it will display all the output columns. Also
> you may shorten the gap between start and end lsn to reduce the output
> size.

All columns are giving huge output, especially because of data and
description columns hence I'm not showing them in the sample output.

> ==
>
> Any reason for not specifying author name in the .sgml file. Do you
> want me to add my name to the author? :)

Haha. Thanks. I will add in the v9 patch set which I will post in a while.

Regards,
Bharath Rupireddy.