Fix: pgxpool: background health check cannot overflow pool

It was previously possible for a connection to be created while the
background health check was running. The health check could create
connection(s) in excess of the maximum pool size in this case.

#1660

go.mod

@@ -5,7 +5,7 @@ go 1.19
 require (
 	github.com/jackc/pgpassfile v1.0.0
 	github.com/jackc/pgservicefile v0.0.0-20221227161230-091c0ba34f0a
-	github.com/jackc/puddle/v2 v2.2.0
+	github.com/jackc/puddle/v2 v2.2.1
 	github.com/stretchr/testify v1.8.1
 	golang.org/x/crypto v0.9.0
 	golang.org/x/sys v0.8.0

go.sum

@@ -8,6 +8,8 @@ github.com/jackc/pgservicefile v0.0.0-20221227161230-091c0ba34f0a h1:bbPeKD0xmW/
 github.com/jackc/pgservicefile v0.0.0-20221227161230-091c0ba34f0a/go.mod h1:5TJZWKEWniPve33vlWYSoGYefn3gLQRzjfDlhSJ9ZKM=
 github.com/jackc/puddle/v2 v2.2.0 h1:RdcDk92EJBuBS55nQMMYFXTxwstHug4jkhT5pq8VxPk=
 github.com/jackc/puddle/v2 v2.2.0/go.mod h1:vriiEXHvEE654aYKXXjOvZM39qJ0q+azkZFrfEOc3H4=
+github.com/jackc/puddle/v2 v2.2.1 h1:RhxXJtFG022u4ibrCSMSiu5aOq1i77R3OHKNJj77OAk=
+github.com/jackc/puddle/v2 v2.2.1/go.mod h1:vriiEXHvEE654aYKXXjOvZM39qJ0q+azkZFrfEOc3H4=
 github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=
 github.com/kr/pretty v0.2.1/go.mod h1:ipq/a2n7PKx3OHsz4KJII5eveXtPO4qwEXGdVfWzfnI=
 github.com/kr/pretty v0.3.0 h1:WgNl7dwNpEZ6jJ9k1snq4pZsg7DOEN8hP9Xw0Tsjwk0=

pgxpool/pool.go

@@ -477,6 +477,10 @@ func (p *Pool) createIdleResources(parentCtx context.Context, targetResources in
 		go func() {
 			atomic.AddInt64(&p.newConnsCount, 1)
 			err := p.p.CreateResource(ctx)
+			// Ignore ErrNotAvailable since it means that the pool has become full since we started creating resource.
+			if err == puddle.ErrNotAvailable {
+				err = nil
+			}
 			errs <- err
 		}()
 	}