Horton

Re: sync()

Bruce Momjian <pgman@candle.pha.pa.us>

View thread
From: Bruce Momjian <pgman@candle.pha.pa.us>
To: Tatsuo Ishii <t-ishii@sra.co.jp>
Cc: pgsql-hackers@postgresql.org
Date: 2003-01-08T06:18:35Z
Lists: pgsql-hackers 
Tatsuo Ishii wrote:
> I noticed sync() is used in PostgreSQL.
> 
> CHECKPOINT -> FlushBufferPool() -> smgrsync() -> mdsync() -> sync()
> 
> Can someone tell me why we need sync() here?

As part of checkpoint, we discard some WAL files.  To do that, we must
first be sure that all the dirty buffers we have written to the kernel
are actually on the disk.  That is why the sync() is required.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073