[Pgpool-general] questions about poolin, load balancing and other things

[Marcelo Martins]

Hi Tatsuo,

I understand that pgpool does pooling by saving the connections to PG  
and reusing them when the same user/database is used and indeed I see  
some pcp procs being reused 40+ times.  What I'm trying to figure out  
here is, does pgpool just passes the new query it receives through  
that same connection that has already been opened previously and such  
will be reused by this new request coming from the same user to the  
same database ?

How does pgpool queues its incoming connections when it starts to  
receive more connections than num_init_children is available ? I'm  
pretty sure here that the "child_life_time" setting would be the one  
responsible for freeing up the pgpool a  child so that the new  
connection queued can obtain access to PG through pgpool and execute  
its query, correct ?

In regards to the load balancing, that can indeed be very helpful  
specially since the master node is usually the one with a higher load.  
I'm pretty sure this may not be possible right now but it would be  
pretty cool if pgpool only opened a connection to the backend that it  
chooses to run the SELECT query against. I'm pretty sure this may be  
complicated to implement, if it all possible which may not be,  since  
this would affect how pgpool handles connections.


Also you were right about the online recovery scripts. If I skip the  
second base backup it seems 30-50% faster in most cases. What takes  
the longest time is just the checkpoint that pg_start_backup has to do  
while there is a lot of writes are being done to the DB. But the new  
online recovery setting makes things perfect since the client just  
keeps on trying to send the data over and eventually when the 2nd  
stage is over the rest of all data resumes to be sent.

can't remember the other questions right now, sorry :)




Marcelo
PostgreSQL DBA
Linux/Solaris System Administrator
http://www.zeroaccess.org