Re: [PATCH] Refactor: Extract XLogRecord info

Steven Niu <niushiji@gmail.com> 于2025年6月10日周二 17:56写道：

> I'm confused by the code of XLR_RMGR_INFO_MASK and XLR_INFO_MASK.
>
> According to the definition of masks, the high 4 bits are for rmgr.
>
> /*
>  * The high 4 bits in xl_info may be used freely by rmgr. The
>  * XLR_SPECIAL_REL_UPDATE and XLR_CHECK_CONSISTENCY bits can be passed by
>  * XLogInsert caller. The rest are set internally by XLogInsert.
>  */
> #define XLR_INFO_MASK 0x0F
> #define XLR_RMGR_INFO_MASK 0xF0
>
>
> However, in function XLogInsert(), there is code:
>
> /*
> * The caller can set rmgr bits, XLR_SPECIAL_REL_UPDATE and
> * XLR_CHECK_CONSISTENCY; the rest are reserved for use by me.
> */
> if ((info & ~(XLR_RMGR_INFO_MASK |
>  XLR_SPECIAL_REL_UPDATE |
>  XLR_CHECK_CONSISTENCY)) != 0)
> elog(PANIC, "invalid xlog info mask %02X", info);
>
> XLogInsert only allows the  rmgr ,XLR_SPECIAL_REL_UPDATE and
XLR_CHECK_CONSISTENCY
set in the info.

> #define XLR_SPECIAL_REL_UPDATE 0x01
> #define XLR_CHECK_CONSISTENCY 0x02
>
> As the XLR_SPECIAL_REL_UPDATE and XLR_CHECK_CONSISTENCY are of the low 4
> bits,
> the above code is indicating the low 4 bits are for rmgr too?
>

No, only the high 4 bits are used for RMGR, see the code under directory
'src/backend/access/rmgrdesc'

 'XLR_SPECIAL_REL_UPDATE' and 'XLR_CHECK_CONSISTENCY' are not RMGR info,
but they
can be passed by XLogInsert caller.

>
>
> Did I misunderstand something?
>
> Thanks，
> Steven
>

-- 
Best regards !
Xiaoran Wang