Tagging with oslo as this sounds related to oslo.db.
On 9/5/19 7:37 PM, Albert Braden wrote:
After more googling it appears that max_pool_size is a maximum limit on the number of connections that can stay open, and max_overflow is a maximum limit on the number of connections that can be temporarily opened when the pool has been consumed. It looks like the defaults are 5 and 10 which would keep 5 connections open all the time and allow 10 temp.
Do I need to set max_pool_size to 0 and max_overflow to the number of connections that I want to allow? Is that a reasonable and correct configuration? Intuitively that doesn't seem right, to have a pool size of 0, but if the "pool" is a group of connections that will remain open until they time out, then maybe 0 is correct?
I don't think so. According to [0] and [1], a pool_size of 0 means unlimited. You could probably set it to 1 to minimize the number of connections kept open, but then I expect you'll have overhead from having to re-open connections frequently.
It sounds like you could use a NullPool to eliminate connection pooling entirely, but I don't think we support that in oslo.db. Based on the error message you're seeing, I would take a look at connection_recycle_time[2]. I seem to recall seeing a comment that the recycle time needs to be shorter than any of the timeouts in the path between the service and the db (so anything like haproxy or mysql itself). Shortening that, or lengthening intervening timeouts, might get rid of these disconnection messages.
0: https://docs.openstack.org/oslo.db/stein/reference/opts.html#database.max_po... 1: https://docs.sqlalchemy.org/en/13/core/pooling.html#sqlalchemy.pool.QueuePoo... 2: https://docs.openstack.org/oslo.db/stein/reference/opts.html#database.connec...
*From:* Albert Braden Albert.Braden@synopsys.com *Sent:* Wednesday, September 4, 2019 10:19 AM *To:* openstack-discuss@lists.openstack.org *Cc:* Gaëtan Trellu gaetan.trellu@incloudus.com *Subject:* RE: Nova causes MySQL timeouts
We’re not setting max_pool_size nor max_overflow option presently. I googled around and found this document:
https://docs.openstack.org/keystone/stein/configuration/config-options.html https://urldefense.proofpoint.com/v2/url?u=https-3A__docs.openstack.org_keystone_stein_configuration_config-2Doptions.html&d=DwMGaQ&c=DPL6_X_6JkXFx7AXWqB0tg&r=XrJBXYlVPpvOXkMqGPz6KucRW_ils95ZMrEmlTflPm8&m=3eF4Bv1HRQW6gl7II12rTTSKj_A9_LDISS6hU0nP-R0&s=0EGWx9qW60G1cxoPFCIv_G1-iXX20jKcC5-AwlCWk8g&e=
Document says:
[api_database]
connection_recycle_time = 3600 (Integer) Timeout before idle SQL connections are reaped.
max_overflow = None (Integer) If set, use this value for max_overflow with SQLAlchemy.
max_pool_size = None (Integer) Maximum number of SQL connections to keep open in a pool.
[database]
connection_recycle_time = 3600 (Integer) Timeout before idle SQL connections are reaped.
min_pool_size = 1 (Integer) Minimum number of SQL connections to keep open in a pool.
max_overflow = 50 (Integer) If set, use this value for max_overflow with SQLAlchemy.
max_pool_size = None (Integer) Maximum number of SQL connections to keep open in a pool.
If min_pool_size is >0, would that cause at least 1 connection to remain open until it times out? What are the recommended values for these, to allow unused connections to close before they time out? Is “min_pool_size = 0” an acceptable setting?
My settings are default:
[api_database]:
#connection_recycle_time = 3600
#max_overflow = <None>
#max_pool_size = <None>
[database]:
#connection_recycle_time = 3600
#min_pool_size = 1
#max_overflow = 50
#max_pool_size = 5
It’s not obvious what max_overflow does. Where can I find a document that explains more about these settings?
*From:* Gaëtan Trellu <gaetan.trellu@incloudus.com mailto:gaetan.trellu@incloudus.com> *Sent:* Tuesday, September 3, 2019 1:37 PM *To:* Albert Braden <albertb@synopsys.com mailto:albertb@synopsys.com> *Cc:* openstack-discuss@lists.openstack.org mailto:openstack-discuss@lists.openstack.org *Subject:* Re: Nova causes MySQL timeouts
Hi Albert,
It is a configuration issue, have a look to max_pool_size and max_overflow options under [database] section.
Keep in mind than more workers you will have more connections will be opened on the database.
Gaetan (goldyfruit)
On Sep 3, 2019 4:31 PM, Albert Braden <Albert.Braden@synopsys.com mailto:Albert.Braden@synopsys.com> wrote:
It looks like nova is keeping mysql connections open until they time out. How are others responding to this issue? Do you just ignore the mysql errors, or is it possible to change configuration so that nova closes and reopens connections before they time out? Or is there a way to stop mysql from logging these aborted connections without hiding real issues? Aborted connection 10726 to db: 'nova' user: 'nova' host: 'asdf' (Got timeout reading communication packets)