Обсуждение: pg_isready docs doesn't specify what exactly it is checking
The following documentation comment has been logged on the website: Page: https://www.postgresql.org/docs/14/app-pg-isready.html Description: `pg_isready` docs don't specify how its different from a port probe - what does on top of checking that a port is open? Does it send some handshake message that a server responds to when initialization is finished? People here are telling that `pg_isready` is not reliable and that `pg_isready` may return when database is not actually ready https://github.com/docker-library/postgres/issues/880#issuecomment-1004251102 Without further info about `pg_isready` it is not clear if it should be filled as a bug. Or if it should be filled as a bug only when an initialization script is involved.
On Tue, Jan 4, 2022, at 3:11 PM, PG Doc comments form wrote:
`pg_isready` docs don't specify how its different from a port probe - whatdoes on top of checking that a port is open? Does it send some handshakemessage that a server responds to when initialization is finished?
pg_isready uses a PQping function that reports the current Postgres status. The
main advantage of pg_isready is that it uses the Postgres protocol to report
the server status. A port probe is not a sufficient step to determine if the
server is running and accepting connections. Why? A Postgres server can be
running but in a state that disallows connections such as during a startup or
crash recovery phase. pg_isready is capable of reporting such state
(PQPING_REJECT -- 1) [1].
We could include a sentence explaining that a port probe is not a sufficient
condition to successfully connect to a Postgres server because the state
machine has more than 2 states. PQping [1] already states "reports the status
of the server" and describe each state it provides. Feel free to suggest an
improvement to documentation.
People here are telling that `pg_isready` is not reliable and that`pg_isready` may return when database is not actually readyWithout further info about `pg_isready` it is not clear if it should befilled as a bug. Or if it should be filled as a bug only when aninitialization script is involved.
There is no known issues with pg_isready and that report isn't clear. He says
"database and/or user wasn't available". What's the exact error message? If
there is a reproducible test case, share it here.
On Fri, 7 Jan 2022 at 03:29, Euler Taveira <euler@eulerto.com> wrote:
On Tue, Jan 4, 2022, at 3:11 PM, PG Doc comments form wrote:We could include a sentence explaining that a port probe is not a sufficientcondition to successfully connect to a Postgres server because the statemachine has more than 2 states. PQping [1] already states "reports the statusof the server" and describe each state it provides. Feel free to suggest animprovement to documentation.
A diagram of the state machine would be very useful.
There is no known issues with pg_isready and that report isn't clear. He says"database and/or user wasn't available". What's the exact error message? Ifthere is a reproducible test case, share it here.
PostgreSQL docker image can run initialization scripts at container start to
create database, users and maybe load some data. So when pg_isready
reports success, the DB can still be in an inconsistent state for an app to start
using it.
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Anatoli Babenia