[pgpool-general: 5481] Re: max_pool parameter question (again!)

[Piotr Gbyliczek]

On Monday, 15 May 2017 18:58:45 BST Pierre Timmermans wrote:
> Hi,
> This question was asked recently (thread 5439) but I don't understand the
> answer (I cannot reply to this thread because I was not yet subscribed). So
> I still cannot understand when the  max_pool parameter is taken into
> consideration by pgpool Like in the initial question, I experimented with
> num_init_children=1 and max_pool=2 If I connect with userA, then obviously
> it works. Then, in another window, I connect with userB : but it hangs
> (until I disconnect userA). My understanding of max_pool was that each
> children could cache 2 connections, one for each database user.


You are missing the fact that num_init_children limits your connections from 
client to pgpool. Each child can serve one connection in at the time.

So, you have 2 connection pools to backend servers, but you only allow one 
connection to pgpool, making the second pool utterly pointless. 

Number of pools regulates how often the new connection will benefit from 
already open cached connection to backend, or in other words, how often it 
will suffer from the delay of new backend connections being established. 

For example, if you have an user connecting to 3 databases, then you have 3 
distinctive user/database pairs. It would be best to set max_pool to 3. 
Setting it at 2 as above means that there is 33% chance that new connection 
will have to be established to backend servers (and it will be cached as such 
from that moment).

Regards,
Piotr
--

Piotr Gbyliczek
Solutions Engineer

Node4 Ltd, The POD, 10 Bottle Ln, Nottingham NG1 2HL
ddi. 08454 210444 | t. 0845 123 2222
e. P.Gbyliczek at node4.co.uk



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