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help / color / mirror / Atom feedFrom: Lakshmi N <[email protected]>
To: Amit Langote <[email protected]>
Cc: [email protected] <[email protected]>
Cc: [email protected]
Subject: Re: Reject invalid databases in pg_get_database_ddl()
Date: Thu, 16 Apr 2026 09:46:45 -0700
Message-ID: <CA+3i_M8Mq7fr6mUspSa2rLik9+oY4sOeD1qsB_-dvnUB4NrYbg@mail.gmail.com> (raw)
In-Reply-To: <CA+HiwqH+0rgMNQDog0AT9dVt0CGjXza_Li80njDhynWqzUwvZw@mail.gmail.com>
References: <CA+3i_M8m1k2gFch+tU0JmAQh9FRV+pFrfTXDrJo+BqmwsTmOhg@mail.gmail.com>
<CA+HiwqH+0rgMNQDog0AT9dVt0CGjXza_Li80njDhynWqzUwvZw@mail.gmail.com>
Hi Amit,
On Thu, Apr 16, 2026 at 2:29 AM Amit Langote <[email protected]>
wrote:
> Hi,
>
> On Thu, Apr 16, 2026 at 5:20 PM Lakshmi N <[email protected]> wrote:
> > pg_get_database_ddl() is not checking for databases in an invalid state
> > before producing ddl statements. This caused the function to emit
> > CONNECTION_LIMIT = -2, which is invalid SQL that Postgres rejects.
> > A database row can be in this inconsistent state longer, for example
> > server crashed during a drop database.
> >
> > Attached patch to fix this issue by doing a database_is_invalid_form()
> > check early in pg_get_database_ddl_internal().
>
> Thanks for the report.
>
> Hmm, I see that the function will happily emit datconnlimit = -2 and
> your patch catches that at the top instead of down below near this
> code:
>
> /* CONNECTION LIMIT */
> if (dbform->datconnlimit != -1)
> {
> resetStringInfo(&buf);
> appendStringInfo(&buf, "ALTER DATABASE %s CONNECTION LIMIT = %d;",
> quote_identifier(dbname), dbform->datconnlimit);
> statements = lappend(statements, pstrdup(buf.data));
> }
>
> which, I guess, makes sense.
>
> The comment is correct but could be more explicit:
>
> /*
> * Reject invalid databases: datconnlimit = -2 would be emitted as
> * CONNECTION LIMIT = -2, which fails on replay.
> */
>
Thank you for reviewing! Please find the attached v2 addressing this.
Regards,
Lakshmi
Attachments:
[application/octet-stream] v2-0001-Reject-pg_get_database_ddl-for-invalid-databases.patch (901B, 3-v2-0001-Reject-pg_get_database_ddl-for-invalid-databases.patch)
download | inline diff:
diff --git a/src/backend/utils/adt/ddlutils.c b/src/backend/utils/adt/ddlutils.c
index c4f9f86c43e..533fc8c9f9c 100644
--- a/src/backend/utils/adt/ddlutils.c
+++ b/src/backend/utils/adt/ddlutils.c
@@ -887,6 +887,17 @@ pg_get_database_ddl_internal(Oid dbid, bool pretty,
dbform = (Form_pg_database) GETSTRUCT(tuple);
dbname = pstrdup(NameStr(dbform->datname));
+ /*
+ * Reject invalid databases: datconnlimit = -2 would be emitted as
+ * CONNECTION LIMIT = -2, which fails on replay.
+ */
+ if (database_is_invalid_form(dbform))
+ ereport(ERROR,
+ (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+ errmsg("cannot generate DDL for invalid database \"%s\"",
+ dbname),
+ errhint("Use DROP DATABASE to drop invalid databases.")));
+
/*
* We don't support generating DDL for system databases. The primary
* reason for this is that users shouldn't be recreating them.
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Subject: Re: Reject invalid databases in pg_get_database_ddl()
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