Re: Wrong statistics for size of XLOG_SWITCH during pg_waldump.

Thanks for all the suggestions.

>Yeah. In its current shape, it means that only pg_waldump would be
>able to know this information. If you make this information part of
>xlogdesc.c, any consumer of the WAL record descriptions would be able
>to show this information, so it would provide a consistent output for
>any kind of tools.
I have change the implement, move some code into xlog_desc().

>On top of that, it seems to me that the calculation used in the patch
>is wrong in two aspects at quick glance:
>1) startSegNo and endSegNo point always to two different segments with
>a XLOG_SWITCH record, so you should check that ReadRecPtr is not at a
>segment border instead before extracting SizeOfXLogLongPHD, no?
Yes you are right, and I use 'record->EndRecPtr - 1' instead.

>2) This stuff should also check after the case of a WAL *page* border
>where you'd need to adjust based on SizeOfXLogShortPHD instead.
The 'junk_len -= SizeOfXLogLongPHD' code is considered for when the
remain size of a wal segment can not afford a XLogRecord struct for
XLOG_SWITCH, it needn't care *page* border.

>I'm not sure the exact motive of this proposal, but if we show the
>wasted length in the stats result, I think it should be other than
>existing record types.
Yes agree, and now it looks like below as new patch:

movead(at)movead-PC:/h2/pg/bin$ ./pg_waldump -p ../walbk/ -s 0/3000000 -e 0/6000000 -z
Type N (%) Record size (%) FPI size (%) Combined size (%)
---- - --- ----------- --- -------- --- ------------- ---
XLOG 5 ( 31.25) 300 ( 0.00) 0 ( 0.00) 300 ( 0.00)
XLOGSwitchJunk 3 ( 18.75) 50330512 (100.00) 0 ( 0.00) 50330512 (100.00)

movead(at)movead-PC:/h2/pg/bin$ ./pg_waldump -p ../walbk/ -s 0/3000000 -e 0/6000000 --stat=record
XLOG/SWITCH 3 ( 18.75) 72 ( 0.00) 0 ( 0.00) 72 ( 0.00)
XLOG/SWITCH_JUNK 3 ( 18.75) 50330512 (100.00) 0 ( 0.00) 50330512 (100.00)

The shortcoming now is I do not know how to handle the 'count' of SWITCH_JUNK
in pg_waldump results. Currently I regard SWITCH_JUNK as one count.

>By the way, I noticed that --stats=record shows two lines for
>Transaction/COMMIT. The cause is that XLogDumpCountRecord assumes the
>all four bits of xl_info is used to identify record id.
Thanks,I didn't notice it before, and your patch added into v3 patch attached.

Regards,
Highgo Software (Canada/China/Pakistan)
URL : www.highgo.ca
EMAIL: mailto:movead(dot)li(at)highgo(dot)ca