Thread

1. lock mode for ControlFileLock which pg_start_backup uses

   Fujii Masao <masao.fujii@gmail.com> — 2010-03-09T01:33:42Z

   Hi,
   
   Currently pg_start_backup() accesses the shared ControlFile
   by using ControlFileLock with LW_EXCLUSIVE lock mode. But
   since that access is read-only operation, LW_SHARED should
   be chosen instead of LW_EXCLUSIVE.
   
   The attached patch changes the lock mode which pg_start_backup()
   uses. Is it worth applying this patch?
   
   Regards,
   
   -- 
   Fujii Masao
   NIPPON TELEGRAPH AND TELEPHONE CORPORATION
   NTT Open Source Software Center
   

2. Re: lock mode for ControlFileLock which pg_start_backup uses

   Takahiro Itagaki <itagaki.takahiro@oss.ntt.co.jp> — 2010-03-09T07:47:21Z

   Fujii Masao <masao.fujii@gmail.com> wrote:
   
   > Currently pg_start_backup() accesses the shared ControlFile
   > by using ControlFileLock with LW_EXCLUSIVE lock mode. But
   > since that access is read-only operation, LW_SHARED should
   > be chosen instead of LW_EXCLUSIVE.
   
   Almost all operations of ControlFileLock is in LW_EXCLUSIVE, but
   there is one usage of LWLockConditionalAcquire(ControlFileLock, LW_SHARED)
   in XLogNeedsFlush().
   
   > The attached patch changes the lock mode which pg_start_backup()
   > uses. Is it worth applying this patch?
   
   I think the patch is reasonable to represent what we are doing,
   even if there is no performance benefits from it.
   
   Regards,
   ---
   Takahiro Itagaki
   NTT Open Source Software Center
   
   
   
   

3. Re: lock mode for ControlFileLock which pg_start_backup uses

   Heikki Linnakangas <heikki.linnakangas@enterprisedb.com> — 2010-03-09T09:56:23Z

   Takahiro Itagaki wrote:
   > Fujii Masao <masao.fujii@gmail.com> wrote:
   >> The attached patch changes the lock mode which pg_start_backup()
   >> uses. Is it worth applying this patch?
   > 
   > I think the patch is reasonable to represent what we are doing,
   > even if there is no performance benefits from it.
   
   Agreed.
   
   -- 
     Heikki Linnakangas
     EnterpriseDB   http://www.enterprisedb.com
   
   

4. Re: lock mode for ControlFileLock which pg_start_backup uses

   Takahiro Itagaki <itagaki.takahiro@oss.ntt.co.jp> — 2010-03-10T02:09:40Z

   Fujii Masao <masao.fujii@gmail.com> wrote:
   
   > Currently pg_start_backup() accesses the shared ControlFile
   > by using ControlFileLock with LW_EXCLUSIVE lock mode. But
   > since that access is read-only operation, LW_SHARED should
   > be chosen instead of LW_EXCLUSIVE.
   > 
   > The attached patch changes the lock mode which pg_start_backup()
   > uses. Is it worth applying this patch?
   
   Thanks, applied.
   
   Regards,
   ---
   Takahiro Itagaki
   NTT Open Source Software Center