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From: Fujii Masao <[email protected]>
To: Takahiro Itagaki <[email protected]>
Cc: PostgreSQL-development <[email protected]>
Subject: Re: Re: [BUGS] BUG #4566: pg_stop_backup() reports incorrect STOP WAL LOCATION
Date: Tue, 16 Feb 2010 14:19:15 +0900
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
	<[email protected]>
	<[email protected]>

On Fri, Feb 5, 2010 at 9:08 AM, Takahiro Itagaki
<[email protected]> wrote:
>
> Fujii Masao <[email protected]> wrote:
>
>> On Fri, Dec 5, 2008 at 11:41 PM, Randy Isbell <[email protected]> wrote:
>> > An inconsistency exists between the segment name reported by
>> > pg_stop_backup() and the actual WAL file name.
>> >
>> > START WAL LOCATION: 10/FE1E2BAC (file 0000000200000010000000FE)
>> > STOP WAL LOCATION: 10/FF000000 (file 0000000200000010000000FF)
>
>> But it was rejected because its change might break the existing app.
>
> It might break existing applications if it returns "FE" instead of "FF",
> but never-used filename surprises users. (IMO, the existing apps probably
> crash if "FF" returned, i.e, 1/256 of the time.)
>
> Should it return the *next* reasonable log filename instead of "FF"?
> For example, 000000020000002000000000 for the above case.

Here is the patch that avoids a nonexistent file name, according to
Itagaki-san's suggestion. If we are crossing a logid boundary, the
next reasonable file name is used instead of a nonexistent one.

Regards,

-- 
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center


Attachments:

  [text/x-patch] stop_file_name_0216.patch (1.0K, 2-stop_file_name_0216.patch)
  download | inline diff:
*** a/src/backend/access/transam/xlog.c
--- b/src/backend/access/transam/xlog.c
***************
*** 8057,8063 **** pg_stop_backup(PG_FUNCTION_ARGS)
  	 */
  	RequestXLogSwitch();
  
! 	XLByteToSeg(stoppoint, _logId, _logSeg);
  	XLogFileName(stopxlogfilename, ThisTimeLineID, _logId, _logSeg);
  
  	/* Use the log timezone here, not the session timezone */
--- 8057,8078 ----
  	 */
  	RequestXLogSwitch();
  
! 	if (stoppoint.xrecoff >= XLogSegSize)
! 	{
! 		XLogRecPtr	recptr = stoppoint;
! 
! 		/*
! 		 * Since xlog segment file name is calculated by using XLByteToSeg,
! 		 * it might indicate a nonexistent file (i.e., which ends in "FF")
! 		 * when we are crossing a logid boundary. In this case, we use the
! 		 * next reasonable file name instead of nonexistent one.
! 		 */
! 		recptr.xlogid += 1;
! 		recptr.xrecoff = XLOG_BLCKSZ;
! 		XLByteToSeg(recptr, _logId, _logSeg);
! 	}
! 	else
! 		XLByteToSeg(stoppoint, _logId, _logSeg);
  	XLogFileName(stopxlogfilename, ThisTimeLineID, _logId, _logSeg);
  
  	/* Use the log timezone here, not the session timezone */

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