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prefill after switch-to #224

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fluca1978 opened this issue Apr 28, 2022 · 10 comments
Closed

prefill after switch-to #224

fluca1978 opened this issue Apr 28, 2022 · 10 comments
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@fluca1978
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enhancement Improvement to an existing feature

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@fluca1978
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Don't know if this is a valuable feature, but with 1.5 when I do a switch-to and/or a reset-server the prefill seems to be dropped.
I mean, when I start pgagroal the "initial" connections from pgagroal_databases.conf are established. When I do a switch-to to another server, the new server does not get the "initial" connection number but only the "minimum".
The same when I come back with another switch-to the original server.
Is there a reason or should pgagroal honor the "initial" connection every time a server is changed as primary?
@fluca1978 fluca1978 added the feature New feature label Apr 28, 2022
@jesperpedersen jesperpedersen self-assigned this Apr 28, 2022
@jesperpedersen jesperpedersen added enhancement Improvement to an existing feature and removed feature New feature labels Apr 28, 2022
@jesperpedersen
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I agree. switch-to should trigger prefill, since the connections on the previous primary should go into graceful

@fluca1978
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The problem, at least in my configuration, is when the old server is flushed: https://github.com/agroal/pgagroal/blob/master/src/libpgagroal/pool.c#L852.
There are however other places where the prefill is invoked with a false argument, that measn "use min values", while we would like to get with "initial" values.
I think there is the need to understand if pgagroal_flush_server has been invoked by a flush command, in which case it is correct to set connections to the minimum, or by a switch-to, in such case it should be prefil with "initial".
Adding a parameter to the pgagroal_flush_server?

@jesperpedersen
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That is likely one way to do it

@fluca1978
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I could spend some time and effort on this, if you believe there are no other tricks and dangerous zones...

@jesperpedersen
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Go for it !

@jesperpedersen
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There is a bit more to it.

The old primary should never prefill no matter what the min_size is - in the case of switch-to.

@fluca1978
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The old primary should never prefill no matter what the min_size is - in the case of switch-to.

I'm going to work on this starting from the next week, but in the meantime I'm reasoning about this.
When I switch-to a new server, the old primary will be graceful and the new one is going to get prefilled, and this is the problem I'm going to try to fix. If I then switch-to back to the old primary, why should I don't prefill it?

@jesperpedersen
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In relation to the switch-to.

pgagroal_databases.conf

mydb myuser 100 20 10

Initial

host1(20)(Primary)
host2(0)(Not init)

switch-to(host2)

host1(0)(Not init)
host2(20)(Primary)

switch-to(host1)

host1(20)(Primary)
host2(0)(Not init)

So, I think we agree, right ?

@fluca1978
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Yes, it was what I was thinking about.

@jesperpedersen
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👍

fluca1978 added a commit to fluca1978/pgagroal that referenced this issue May 4, 2022
@fluca1978
[agroal#224] Prefill a new server when doing a switch-to
ce9167b 
When a `switch-to` operation is issued, the old server is flushed
(i.e., connections are closed) and new connections to the new primary
server are established.
When such connections are established, the system does a full prefill
against the new primary, so that when the `switch-to` completes, the
new primary is prefilled as the old one was.

Adds also a better detail about the server that is going to be
flushed.

Close agroal#224
@fluca1978 fluca1978 mentioned this issue May 4, 2022
Closed
fluca1978 added a commit to fluca1978/pgagroal that referenced this issue May 4, 2022
@fluca1978
[agroal#224] Prefill when doing a switch-to or primary change.
b891a9a 
Whenever the primary host is changed, by means of an explicit
`switch-to` command or by a primary failure, the connection flushing
is activated. If possible, the prefill should be also restored on the
new server.
As suggested in
<agroal#225 (comment)>
it would be nice to check if the specified new server is the same as
the old one (failure of the primary) or a different one (`switch-to`),
and in the case they are different the prefill is forced.
fluca1978 added a commit to fluca1978/pgagroal that referenced this issue May 4, 2022
@fluca1978
Rename variables and move check for prefill.
1ed4be7 
See <agroal#226 (comment)>.
Do the check of the new primary in the very beginning.

Improves also the logs in debug mode to clearly indicate what is going
to happen to the old and new server.

Close agroal#224
fluca1978 added a commit to fluca1978/pgagroal that referenced this issue May 5, 2022
@fluca1978
[agroal#224] Prefill when doing a switch-to or primary change.
0143de9 
Whenever the primary host is changed, by means of an explicit
`switch-to` command or by a primary failure, the connection flushing
is activated. If possible, the prefill should be also restored on the
new server.
As suggested in
<agroal#225 (comment)>
it would be nice to check if the specified new server is the same as
the old one (failure of the primary) or a different one (`switch-to`),
and in the case they are different the prefill is forced.

The prefill will always be to the `INITIAL` size when needed.
If the primary is not set, there is no need to prefill
with the `MIN_SIZE` value.

Close agroal#224
fluca1978 added a commit to fluca1978/pgagroal that referenced this issue May 5, 2022
@fluca1978
[agroal#224] Prefill when doing a switch-to or primary change.
a6076a6 
Whenever the primary host is changed, by means of an explicit
`switch-to` command or by a primary failure, the connection flushing
is activated. If possible, the prefill should be also restored on the
new server.
As suggested in
<agroal#225 (comment)>
it would be nice to check if the specified new server is the same as
the old one (failure of the primary) or a different one (`switch-to`),
and in the case they are different the prefill is forced.

The prefill will always be to the `INITIAL` size when needed.
If the primary is not set, there is no need to prefill
with the `MIN_SIZE` value.

Close agroal#224
jesperpedersen pushed a commit that referenced this issue May 6, 2022
@fluca1978 @jesperpedersen
[#224] Prefill when doing a switch-to or primary change.
7cf6293 
Whenever the primary host is changed, by means of an explicit
`switch-to` command or by a primary failure, the connection flushing
is activated. If possible, the prefill should be also restored on the
new server.
As suggested in
<#225 (comment)>
it would be nice to check if the specified new server is the same as
the old one (failure of the primary) or a different one (`switch-to`),
and in the case they are different the prefill is forced.

The prefill will always be to the `INITIAL` size when needed.
If the primary is not set, there is no need to prefill
with the `MIN_SIZE` value.

Close #224
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[#224] Prefill a new server when doing a switch-to fluca1978/pgagroal
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@jesperpedersen @fluca1978