Is this a TODO item? ---------------------------------------------------------------------------
ITAGAKI Takahiro wrote: > "Simon Riggs" <[EMAIL PROTECTED]> wrote: > > > I think what you are saying is: VACUUM places blocks so that they are > > immediately reused. This stops shared_buffers from being polluted by > > vacuumed-blocks, but it also means that almost every write becomes a > > backend dirty write when VACUUM is working, bgwriter or not. That also > > means that we flush WAL more often than we otherwise would. > > That's right. I think it's acceptable that vacuuming process writes dirty > buffers made by itself, because only the process slows down; other backends > can run undisturbedly. However, frequent WAL flushing should be avoided. > > I found the problem when I ran VACUUM FREEZE separately. But if there were > some backends, dirty buffers made by VACUUM would be reused by those backends, > not by the vacuuming process. > > > From above my thinking would be to have a more general implementation: > > Each backend keeps a list of cache buffers to reuse in its local loop, > > rather than using the freelist as a global list. That way the technique > > would work even when we have multiple Vacuums working concurrently. It > > would also then be possible to use this for the SeqScan case as well. > > Great idea! The troubles are in the usage of buffers by SeqScan and VACUUM. > The former uses too many buffers and the latter uses too few buffers. > Your cache-looping will work around both cases. > > > Another connected thought is the idea of a having a FullBufferList - the > > opposite of a free buffer list. When VACUUM/INSERT/COPY fills a block we > > notify the buffer manager that this block needs writing ahead of other > > buffers, so that the bgwriter can work more effectively. That seems like > > it would help with both this current patch and the additional thoughts > > above. > > Do you mean that bgwriter should take care of buffers in freelist, not only > ones in the tail of LRU? We might need activity control of bgwriter. Buffers > are reused rapidly in VACUUM or bulk insert, so bgwriter is not sufficient > if its settings are same as usual. > > Regards, > --- > ITAGAKI Takahiro > NTT Open Source Software Center > > > > ---------------------------(end of broadcast)--------------------------- > TIP 9: In versions below 8.0, the planner will ignore your desire to > choose an index scan if your joining column's datatypes do not > match -- Bruce Momjian [EMAIL PROTECTED] EnterpriseDB http://www.enterprisedb.com + If your life is a hard drive, Christ can be your backup. + ---------------------------(end of broadcast)--------------------------- TIP 2: Don't 'kill -9' the postmaster
