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Thread: pg_isready bug

pg_isready bug

From

"Hunosau, Aliaksei"

Date:

13 April 2020, 15:53:32

We are using Postgres in docker. And problem with pg_isready was found.

Please, look:

root@29243fe45836:/# psql -U postgres

psql (11.6 (Debian 11.6-1.pgdg90+1))

Type "help" for help.

postgres=# \l+

List of databases

-----------+----------+----------+------------+------------+-----------------------+---------+------------+--------------------------------------------

(4 rows)

postgres=# exit

root@29243fe45836:/# pg_isready -d 123456 -h localhost -p 5432 -U postgres # the DB 123456 doesn't exist

localhost:5432 - accepting connections # but it shows all is good

root@29243fe45836:/# echo $?

root@29243fe45836:/# pg_isready -d internal -h localhost -p 5432 -U postgres # the DB internal doesn't exist

localhost:5432 - accepting connections # looks good

root@29243fe45836:/# echo $?

The exitcodes of pg_isready if the DB doesn't exist and if exists are the same.

It will be better to exit with non null exitcode if pg_isready can't connect to absent db or using incorrect user.

Best regards,

Aliaksei Hunosau, DevOps engineer
ScienceSoft - Professional Software Development
2 Bedy Street, Minsk, Belarus, 220040
P +375 17 293 37 36 | F+375 17 293 37 39
ahunosau@scnsoft.com
www.scnsoft.com | LinkedIn | Facebook | Twitter

Re: pg_isready bug

From

Fabien COELHO

Date:

13 April 2020, 17:17:21

Hello,

> root@29243fe45836:/# pg_isready -d 123456 -h localhost -p 5432 -U postgres # the DB 123456 doesn't exist
> localhost:5432 - accepting connections # but it shows all is good
> root@29243fe45836:/# echo $?
> 0

I can confirm, but I'm afraid it is a feature.

The server *is* indeed accepting connections… it does not say that the 
connection with the parameters you supplied worked.

The feature relies on "PQpingParams" function which states the following 
somehow strange sentence:

"It is not necessary to supply correct user name, password, or database 
name values to obtain the server status; however, if incorrect values are 
provided, the server will log a failed connection attempt."

The same occurs with a non existing user (-U).

Basically a connection is merely attempted, but it does not report success 
of said connection. The sentence of "pg_isready --help" is somehow 
ambiguous:

"pg_isready issues a connection check to a PostgreSQL database.", but no 
one specified whaa a "connection check" is. I can understand that you 
would expect to be an actual connection:-)

ISTM that the doc should be clarified about what is a "connection check", 
and that it is not working a connection.

If you want to check that your parameters are ok, probably you want to 
issue an actual psql run, eg:

     psql <my param> -c "SELECT 'ok'"

-- 
Fabien.

Re: pg_isready bug

From

Michael Paquier

Date:

14 April 2020, 03:33:37

On Mon, Apr 13, 2020 at 04:17:21PM +0200, Fabien COELHO wrote:
> Basically a connection is merely attempted, but it does not report success
> of said connection. The sentence of "pg_isready --help" is somehow
> ambiguous:
>
> "pg_isready issues a connection check to a PostgreSQL database.", but no one
> specified whaa a "connection check" is. I can understand that you would
> expect to be an actual connection:-)
>
> ISTM that the doc should be clarified about what is a "connection check",
> and that it is not working a connection.

Yeah, that matches my impression when reading this thread.  Perhaps
the docs had better emphasize that --timeout is a simple mapping for
the connection parameter connect_timeout in this case?  My point is
that the logic tells us that the timeout is in effect when a
connection has been started, but not completed yet.  And the docs of
pg_isready tell us that:
"The maximum number of seconds to wait when attempting connection
before returning that the server is not responding."

So this does not really insist on the point that a timeout has no
effect on a connection immediately failing because of an incorrect
parameter set.
--
Michael

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