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[#224] Prefill a new server when doing a switch-to #225

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[#224] Prefill a new server when doing a switch-to #225

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fluca1978
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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 #224

@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
@jesperpedersen
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Looking at it - there are 2 places where pgagroal_flush_server is called from - 1) The failover scenario, and 2) An unresponsive primary.

For 1) we know that a new primary has been selected. For 2) we know that the primary is the same.

So, I think we can just change pgagroal_flush_server to check for the primary (pgagroal_get_primary) and if it is different than the value passed in invoke pgagroal_prefill(true). That way we don't have to change the function signatures, and it should be a 3-4 line patch :)

Thoughts ?

@jesperpedersen jesperpedersen added the enhancement Improvement to an existing feature label May 4, 2022
fluca1978 added a commit to fluca1978/pgagroal that referenced this pull request 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 fluca1978 mentioned this pull request May 4, 2022
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@fluca1978
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I've crated #226 as a possible implementation of your suggestion.
One thing I don't understand is why pgagroal_flush_server accepts a unsigned char as a server index, while other parts like pgagroal_get_primary handles an integer.
I've inserted a check in the extraction of the new primary, that could be avoided since if pgagroal_get_primary fails we don't need to prefill in any case, but the code looks stronger.

@jesperpedersen
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The pgagroal_get_server uses an integer as its out parameter to highlight that the value can be negative if the function fails to find a primary.

@fluca1978
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Got it, thanks.
I'm closing this same PR since #226 looks more what you have in mind.

@fluca1978 fluca1978 closed this May 4, 2022
fluca1978 added a commit to fluca1978/pgagroal that referenced this pull request 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 pull request 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 pull request May 6, 2022
@fluca1978 @jesperpedersen
[#224] Prefill when doing a switch-to or primary change.
ea00b3a 
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
jesperpedersen pushed a commit that referenced this pull request 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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prefill after switch-to
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