Re: wal_dump output on CREATE DATABASE

Le ven. 2 nov. 2018 à 08:37, Peter Eisentraut <
peter(dot)eisentraut(at)2ndquadrant(dot)com> a écrit :

> On 26/10/2018 15:53, Jean-Christophe Arnu wrote:
> > Exemple on CREATE DATABASE (without defining a template database) :
> > rmgr: Database len (rec/tot): 42/ 42, tx: 568, lsn:
> > 0/01865790, prev 0/01865720, desc: CREATE copy dir 1/1663 to 16384/1663
> >
> > It comes out (to me) it may be more consistent to use the same template
> > than the other operations in pg_waldump.
> > I propose to swap the parameters positions for the copy dir operation
> > output.
> >
> > You'll find a patch file included which does the switching job :
> > rmgr: Database len (rec/tot): 42/ 42, tx: 568, lsn:
> > 0/01865790, prev 0/01865720, desc: CREATE copy dir 1663/1 to 1663/16384
>
> I see your point. I suspect this was mainly implemented that way
> because that's how the fields occur in the underlying
> xl_dbase_create_rec structure. (But that structure also has the target
> location first, so it's not entirely consistent that way either.) We
> could switch the fields around in the output, but I wonder whether we
> couldn't make the whole thing a bit more readable like this:
>
> desc: CREATE copy dir ts=1663 db=1 to ts=1663 db=16384
>
> or maybe like this
>
> desc: CREATE copy dir (ts/db) 1663/1 to 1663/16384
>

Thank you Peter for your review and proposal .
I like the last one which gives the fields semantics in a concise way.
Pushing the idea a bit farther we could think of applying that description
to any other operation that involves the ts/db/oid fields. What do you
think ?

Example in nbtdesc.c we could add the "(ts/db/oid)" information to help the
DBA to identify the objects:
case XLOG_BTREE_REUSE_PAGE:
{
xl_btree_reuse_page *xlrec = (xl_btree_reuse_page *) rec;

appendStringInfo(buf, "rel (ts/db/rel) %u/%u/%u;
latestRemovedXid %u",
xlrec->node.spcNode, xlrec->node.dbNode,
xlrec->node.relNode,
xlrec->latestRemovedXid);
break;
}

This may help DBAs to better identify the objects related to the messages.

Any thought/comments/suggestions ?

~~~ Side story
Well to be clear, my first proposal is born while i was writting a side
script to textually identify which objects were involved into pg_waldump
operations (if that objects already exists at script run time). I'm
wondering whether it could be interesting to incllde such a "textual
decoding" into pg_waldump or not (as a command line switch). Anyway, my
script would be available as proof of concept first. We have time to
discuss that last point in another thread.
~~~

Thank you

>