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help / color / mirror / Atom feedFrom: Hayato Kuroda (Fujitsu) <[email protected]>
To: 'Ted Yu' <[email protected]>
Cc: Katsuragi Yuta <[email protected]>
Cc: Tom Lane <[email protected]>
Cc: vignesh C <[email protected]>
Cc: [email protected] <[email protected]>
Cc: Önder Kalacı <[email protected]>
Cc: Fujii Masao <[email protected]>
Cc: [email protected] <[email protected]>
Cc: Kyotaro Horiguchi <[email protected]>
Subject: RE: [Proposal] Add foreign-server health checks infrastructure
Date: Mon, 23 Jan 2023 05:40:34 +0000
Message-ID: <TYAPR01MB58668DD17F19CAFC97A3134EF5C89@TYAPR01MB5866.jpnprd01.prod.outlook.com> (raw)
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Dear Ted,
Thanks for reviewing! PSA new version.
> For v25-0001-Add-PQConnCheck-and-PQCanConnCheck-to-libpq.patch , `pqConnCheck_internal` only has one caller which is quite short.
> Can pqConnCheck_internal and PQConnCheck be merged into one func ?
I divided the function for feature expandability. Currently it works on linux platform,
but the limitation should be removed in future and internal function will be longer.
Therefore I want to keep this style.
> +int
> +PQCanConnCheck(void)
>
> It seems the return value should be of bool type.
I slightly changed the returned value like true/false. But IIUC libpq functions
cannot define as "bool" datatype. E.g. PQconnectionNeedsPassword() returns true/false,
but the function is defined as int.
Best Regards,
Hayato Kuroda
FUJITSU LIMITED
Attachments:
[application/octet-stream] v26-0001-Add-PQConnCheck-and-PQCanConnCheck-to-libpq.patch (5.0K, ../TYAPR01MB58668DD17F19CAFC97A3134EF5C89@TYAPR01MB5866.jpnprd01.prod.outlook.com/2-v26-0001-Add-PQConnCheck-and-PQCanConnCheck-to-libpq.patch)
download | inline diff:
From 3ad9df1e9c3a6a21268e9599b5b941b047843c72 Mon Sep 17 00:00:00 2001
From: "kuroda.hayato%40jp.fujitsu.com" <[email protected]>
Date: Tue, 1 Nov 2022 09:13:20 +0000
Subject: [PATCH v26 1/3] Add PQConnCheck and PQCanConnCheck to libpq
PQConnCheck() function allows to check the status of socket by polling
the socket. This function is currently available only on systems that
support the non-standard POLLRDHUP extension to the poll system call,
including Linux.
PQCanConnCheck() checks whether above function is available or not.
---
doc/src/sgml/libpq.sgml | 40 ++++++++++++++++++++++
src/interfaces/libpq/exports.txt | 2 ++
src/interfaces/libpq/fe-misc.c | 57 ++++++++++++++++++++++++++++++++
src/interfaces/libpq/libpq-fe.h | 4 +++
4 files changed, 103 insertions(+)
diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 0e7ae70c70..086b97340d 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -2679,6 +2679,46 @@ void *PQgetssl(const PGconn *conn);
</listitem>
</varlistentry>
+ <varlistentry id="libpq-PQConnCheck">
+ <term><function>PQConnCheck</function><indexterm><primary>PQConnCheck</primary></indexterm></term>
+ <listitem>
+ <para>
+ Returns the status of the socket.
+
+<synopsis>
+int PQConnCheck(PGconn *conn);
+</synopsis>
+ </para>
+
+ <para>
+ Unlike <xref linkend="libpq-PQstatus"/>, this function checks socket
+ health. This check is performed by polling the socket. This function is
+ currently available only on systems that support the non-standard
+ <symbol>POLLRDHUP</symbol> extension to the <symbol>poll</symbol> system
+ call, including Linux. <xref linkend="libpq-PQConnCheck"/> returns <literal>1</literal>
+ if the remote peer seems to be closed, returns <literal>0</literal> if
+ the socket is valid, and returns <literal>-1</literal> if the connection
+ has been already invalid.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry id="libpq-PQCanConnCheck">
+ <term><function>PQCanConnCheck</function><indexterm><primary>PQCanConnCheck</primary></indexterm></term>
+ <listitem>
+ <para>
+ Returns whether <xref linkend="libpq-PQConnCheck"/> is available on this
+ platform. <xref linkend="libpq-PQCanConnCheck"/> returns
+ <literal>1</literal> if the function is supported, otherwise returns
+ <literal>0</literal>.
+
+<synopsis>
+int PQCanConnCheck(void);
+</synopsis>
+ </para>
+ </listitem>
+ </varlistentry>
+
</variablelist>
</para>
diff --git a/src/interfaces/libpq/exports.txt b/src/interfaces/libpq/exports.txt
index e8bcc88370..267cfdcb48 100644
--- a/src/interfaces/libpq/exports.txt
+++ b/src/interfaces/libpq/exports.txt
@@ -186,3 +186,5 @@ PQpipelineStatus 183
PQsetTraceFlags 184
PQmblenBounded 185
PQsendFlushRequest 186
+PQConnCheck 187
+PQCanConnCheck 188
diff --git a/src/interfaces/libpq/fe-misc.c b/src/interfaces/libpq/fe-misc.c
index 3653a1a8a6..445a1da721 100644
--- a/src/interfaces/libpq/fe-misc.c
+++ b/src/interfaces/libpq/fe-misc.c
@@ -1218,6 +1218,63 @@ PQenv2encoding(void)
return encoding;
}
+/*
+ * Helper function for PQconnCheck().
+ *
+ * Return >0 if opposite side seems to be disconnected.
+ */
+static int
+pqConnCheck_internal(int sock)
+{
+#if (defined(HAVE_POLL) && defined(POLLRDHUP))
+ struct pollfd input_fd;
+ int errflags = POLLHUP | POLLERR | POLLNVAL;
+
+ input_fd.fd = sock;
+ input_fd.events = POLLRDHUP | errflags;
+ input_fd.revents = 0;
+
+ poll(&input_fd, 1, 0);
+
+ return input_fd.revents;
+#else
+ /* Do not support socket checking on this platform, return 0 */
+ return 0;
+#endif
+}
+
+/*
+ * Check whether the socket peer closed connection or not.
+ *
+ * Returns >0 if remote peer seems to be closed, 0 if it is valid,
+ * -1 if the input connection is bad.
+ */
+int
+PQConnCheck(PGconn *conn)
+{
+ /* quick exit if invalid connection has come */
+ if (conn == NULL ||
+ conn->sock == PGINVALID_SOCKET ||
+ conn->status != CONNECTION_OK)
+ return -1;
+
+ return pqConnCheck_internal(conn->sock);
+}
+
+/*
+ * Check whether PQConnCheck() can work well on this platform.
+ *
+ * Returns 1 if this can use PQConnCheck(), otherwise 0.
+ */
+int
+PQCanConnCheck(void)
+{
+#if (defined(HAVE_POLL) && defined(POLLRDHUP))
+ return true;
+#else
+ return false;
+#endif
+}
#ifdef ENABLE_NLS
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index f3d9220496..053fad0760 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -648,6 +648,10 @@ extern int PQdsplen(const char *s, int encoding);
/* Get encoding id from environment variable PGCLIENTENCODING */
extern int PQenv2encoding(void);
+/* Check whether the postgres server is still alive or not */
+extern int PQConnCheck(PGconn *conn);
+extern int PQCanConnCheck(void);
+
/* === in fe-auth.c === */
extern char *PQencryptPassword(const char *passwd, const char *user);
--
2.27.0
[application/octet-stream] v26-0002-postgres_fdw-add-postgres_fdw_verify_connection_.patch (11.1K, ../TYAPR01MB58668DD17F19CAFC97A3134EF5C89@TYAPR01MB5866.jpnprd01.prod.outlook.com/3-v26-0002-postgres_fdw-add-postgres_fdw_verify_connection_.patch)
download | inline diff:
From c97328f7c6ca16ed4fb5437abd2e2ce8d2d7c27d Mon Sep 17 00:00:00 2001
From: "kuroda.hayato%40jp.fujitsu.com" <[email protected]>
Date: Tue, 1 Nov 2022 09:13:42 +0000
Subject: [PATCH v26 2/3] postgres_fdw: add
postgres_fdw_verify_connection_states
This function can verify the status of connections that are establieshed by
postgres_fdw. This check wil be done by PQConnCheck(), which means this is
available only on systems that support the non-standard POLLRDHUP extension
to the poll system call, including Linux.
This returns true if checked connection is still valid, or the checking is
not supported on this platform. False is returned if the connection seems
to be closed.
---
contrib/postgres_fdw/Makefile | 2 +-
contrib/postgres_fdw/connection.c | 124 ++++++++++++++++++
contrib/postgres_fdw/meson.build | 1 +
.../postgres_fdw/postgres_fdw--1.1--1.2.sql | 19 +++
contrib/postgres_fdw/postgres_fdw.control | 2 +-
doc/src/sgml/postgres-fdw.sgml | 69 ++++++++++
6 files changed, 215 insertions(+), 2 deletions(-)
create mode 100644 contrib/postgres_fdw/postgres_fdw--1.1--1.2.sql
diff --git a/contrib/postgres_fdw/Makefile b/contrib/postgres_fdw/Makefile
index c1b0cad453..6d23768389 100644
--- a/contrib/postgres_fdw/Makefile
+++ b/contrib/postgres_fdw/Makefile
@@ -14,7 +14,7 @@ PG_CPPFLAGS = -I$(libpq_srcdir)
SHLIB_LINK_INTERNAL = $(libpq)
EXTENSION = postgres_fdw
-DATA = postgres_fdw--1.0.sql postgres_fdw--1.0--1.1.sql
+DATA = postgres_fdw--1.0.sql postgres_fdw--1.0--1.1.sql postgres_fdw--1.1--1.2.sql
REGRESS = postgres_fdw
diff --git a/contrib/postgres_fdw/connection.c b/contrib/postgres_fdw/connection.c
index ed75ce3f79..4dc26f48bf 100644
--- a/contrib/postgres_fdw/connection.c
+++ b/contrib/postgres_fdw/connection.c
@@ -86,6 +86,9 @@ static bool xact_got_connection = false;
PG_FUNCTION_INFO_V1(postgres_fdw_get_connections);
PG_FUNCTION_INFO_V1(postgres_fdw_disconnect);
PG_FUNCTION_INFO_V1(postgres_fdw_disconnect_all);
+PG_FUNCTION_INFO_V1(postgres_fdw_verify_connection_states);
+PG_FUNCTION_INFO_V1(postgres_fdw_verify_connection_states_all);
+PG_FUNCTION_INFO_V1(postgres_fdw_can_verify_connection_states);
/* prototypes of private functions */
static void make_new_connection(ConnCacheEntry *entry, UserMapping *user);
@@ -116,6 +119,7 @@ static void pgfdw_finish_pre_subcommit_cleanup(List *pending_entries,
int curlevel);
static bool UserMappingPasswordRequired(UserMapping *user);
static bool disconnect_cached_connections(Oid serverid);
+static bool verify_cached_connections(Oid serverid);
/*
* Get a PGconn which can be used to execute queries on the remote PostgreSQL
@@ -1862,3 +1866,123 @@ disconnect_cached_connections(Oid serverid)
return result;
}
+
+/*
+ * Workhorse to verify cached connections.
+ *
+ * This function scans all the connection cache entries and verifies the
+ * connections whose foreign server OID matches with the specified one. If
+ * InvalidOid is specified, it verifies all the cached connections.
+ *
+ * This function emits warnings if a disconnection is found, and this returns
+ * false only when the lastly verified server seems to be disconnected.
+ *
+ * Note that the verification can be used on some limited platforms. If this
+ * server does not support it, this function alwayse returns true.
+ */
+static bool
+verify_cached_connections(Oid serverid)
+{
+ HASH_SEQ_STATUS scan;
+ ConnCacheEntry *entry;
+ bool all = !OidIsValid(serverid);
+ bool result = true;
+ StringInfoData str;
+
+ /* quick exit if connection cache has not been initialized yet. */
+ if (!ConnectionHash)
+ return true;
+
+ hash_seq_init(&scan, ConnectionHash);
+ while ((entry = (ConnCacheEntry *) hash_seq_search(&scan)))
+ {
+ /* Ignore cache entry if no open connection right now. */
+ if (!entry->conn)
+ continue;
+
+ /* Skip if the entry is invalidated. */
+ if (entry->invalidated)
+ continue;
+
+ if (all || entry->serverid == serverid)
+ {
+ if (PQConnCheck(entry->conn))
+ {
+ /* A foreign server might be down, so construct a message. */
+ ForeignServer *server = GetForeignServer(entry->serverid);
+
+ if (result)
+ {
+ /*
+ * Initialize and add a prefix if this is the first
+ * disconnection we found.
+ */
+ initStringInfo(&str);
+ appendStringInfo(&str, "could not connect to server ");
+
+ result = false;
+ }
+ else
+ appendStringInfo(&str, ", ");
+
+ appendStringInfo(&str, "\"%s\"", server->servername);
+ }
+ }
+ }
+
+ /* Raise a warning if disconnections are found. */
+ if (!result)
+ {
+ Assert(str.len);
+ ereport(WARNING,
+ (errcode(ERRCODE_CONNECTION_FAILURE),
+ errmsg("%s", str.data),
+ errdetail("Socket close is detected."),
+ errhint("Plsease check the health of server.")));
+ pfree(str.data);
+ }
+
+ return result;
+}
+
+/*
+ * Verify the specified cached connections.
+ *
+ * This function verifies the connections that are established by postgres_fdw
+ * from the local session to the foreign server with the given name.
+ *
+ * This function emits a warning if a disconnection is found, and this returns
+ * false only when the verified server seems to be disconnected.
+ *
+ * Note that the verification can be used on some limited platforms. If this
+ * server does not support it, this function alwayse returns true.
+ */
+Datum
+postgres_fdw_verify_connection_states(PG_FUNCTION_ARGS)
+{
+ ForeignServer *server;
+ char *servername;
+
+ servername = text_to_cstring(PG_GETARG_TEXT_PP(0));
+ server = GetForeignServerByName(servername, false);
+
+ PG_RETURN_BOOL(verify_cached_connections(server->serverid));
+}
+
+/*
+ * Verify all the cached connections.
+ *
+ * This function verifies all the connections that are established by postgres_fdw
+ * from the local session to the foreign servers.
+ */
+Datum
+postgres_fdw_verify_connection_states_all(PG_FUNCTION_ARGS)
+{
+ PG_RETURN_BOOL(verify_cached_connections(InvalidOid));
+}
+
+Datum
+postgres_fdw_can_verify_connection_states(PG_FUNCTION_ARGS)
+{
+ PG_RETURN_BOOL(PQCanConnCheck());
+}
diff --git a/contrib/postgres_fdw/meson.build b/contrib/postgres_fdw/meson.build
index 2b451f165e..29118d47bb 100644
--- a/contrib/postgres_fdw/meson.build
+++ b/contrib/postgres_fdw/meson.build
@@ -26,6 +26,7 @@ install_data(
'postgres_fdw.control',
'postgres_fdw--1.0.sql',
'postgres_fdw--1.0--1.1.sql',
+ 'postgres_fdw--1.1--1.2.sql',
kwargs: contrib_data_args,
)
diff --git a/contrib/postgres_fdw/postgres_fdw--1.1--1.2.sql b/contrib/postgres_fdw/postgres_fdw--1.1--1.2.sql
new file mode 100644
index 0000000000..a8556b4c9f
--- /dev/null
+++ b/contrib/postgres_fdw/postgres_fdw--1.1--1.2.sql
@@ -0,0 +1,19 @@
+/* contrib/postgres_fdw/postgres_fdw--1.1--1.2.sql */
+
+-- complain if script is sourced in psql, rather than via ALTER EXTENSION
+\echo Use "ALTER EXTENSION postgres_fdw UPDATE TO '1.2'" to load this file. \quit
+
+CREATE FUNCTION postgres_fdw_verify_connection_states (text)
+RETURNS bool
+AS 'MODULE_PATHNAME'
+LANGUAGE C STRICT PARALLEL RESTRICTED;
+
+CREATE FUNCTION postgres_fdw_verify_connection_states_all ()
+RETURNS bool
+AS 'MODULE_PATHNAME'
+LANGUAGE C STRICT PARALLEL RESTRICTED;
+
+CREATE FUNCTION postgres_fdw_can_verify_connection_states ()
+RETURNS bool
+AS 'MODULE_PATHNAME'
+LANGUAGE C STRICT PARALLEL SAFE;
diff --git a/contrib/postgres_fdw/postgres_fdw.control b/contrib/postgres_fdw/postgres_fdw.control
index d489382064..a4b800be4f 100644
--- a/contrib/postgres_fdw/postgres_fdw.control
+++ b/contrib/postgres_fdw/postgres_fdw.control
@@ -1,5 +1,5 @@
# postgres_fdw extension
comment = 'foreign-data wrapper for remote PostgreSQL servers'
-default_version = '1.1'
+default_version = '1.2'
module_pathname = '$libdir/postgres_fdw'
relocatable = true
diff --git a/doc/src/sgml/postgres-fdw.sgml b/doc/src/sgml/postgres-fdw.sgml
index 644f51835b..05265a1ef8 100644
--- a/doc/src/sgml/postgres-fdw.sgml
+++ b/doc/src/sgml/postgres-fdw.sgml
@@ -826,6 +826,75 @@ postgres=# SELECT postgres_fdw_disconnect_all();
</para>
</listitem>
</varlistentry>
+
+ <varlistentry>
+ <term><function>postgres_fdw_verify_connection_states(server_name text) returns boolean</function></term>
+ <listitem>
+ <para>
+ This function checks the status of remote connections established by
+ <filename>postgres_fdw</filename> from the local session to the foreign
+ server with the given name. This check is performed by polling the socket
+ and allows long-running transactions to be aborted sooner if the kernel
+ reports that the connection is closed. This function is currently
+ available only on systems that support the non-standard <symbol>POLLRDHUP</symbol>
+ extension to the <symbol>poll</symbol> system call, including Linux. This
+ returns <literal>true</literal> if checked connections are still valid,
+ or the checking is not supported on this platform. <literal>false</literal>
+ is returned if the local session seems to be disconnected from other
+ servers. Example usage of the function:
+<screen>
+postgres=# SELECT postgres_fdw_verify_connection_states('loopback1');
+ postgres_fdw_verify_connection_states
+---------------------------------------
+ t
+</screen>
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><function>postgres_fdw_verify_connection_states_all() returns boolean</function></term>
+ <listitem>
+ <para>
+ This function checks the status of all the remote connections established
+ by <filename>postgres_fdw</filename> from the local session to the
+ foreign servers. This check is performed by polling the socket and allows
+ long-running transactions to be aborted sooner if the kernel reports
+ that the connection is closed. This function is currently available only
+ on systems that support the non-standard <symbol>POLLRDHUP</symbol>
+ extension to the <symbol>poll</symbol> system call, including Linux. This
+ returns <literal>true</literal> if all the remote connections are still
+ valid, or the checking is not supported on this platform.
+ <literal>false</literal> is returned if the local session seems to be
+ disconnected from at least one remote server. Example usage of the
+ function:
+<screen>
+postgres=# SELECT postgres_fdw_verify_connection_states_all();
+ postgres_fdw_verify_connection_states_all
+-------------------------------------------
+ t
+</screen>
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><function>postgres_fdw_can_verify_connection_states() returns boolean</function></term>
+ <listitem>
+ <para>
+ This function checks whether functions the health of remote connectio
+ work well or not. This returns <literal>true</literal> if it can be used,
+ otherwise returns <literal>false</literal>. Example usage of the function:
+
+<screen>
+postgres=# SELECT postgres_fdw_can_verify_connection_states();
+ postgres_fdw_can_verify_connection_states
+-------------------------------------------
+ t
+</screen>
+ </para>
+ </listitem>
+ </varlistentry>
+
</variablelist>
</sect2>
--
2.27.0
[application/octet-stream] v26-0003-add-test.patch (4.6K, ../TYAPR01MB58668DD17F19CAFC97A3134EF5C89@TYAPR01MB5866.jpnprd01.prod.outlook.com/4-v26-0003-add-test.patch)
download | inline diff:
From e772dff2ea94ce696c26754f18bd27ef49ab4862 Mon Sep 17 00:00:00 2001
From: "kuroda.hayato%40jp.fujitsu.com" <[email protected]>
Date: Wed, 21 Sep 2022 06:52:23 +0000
Subject: [PATCH v26 3/3] add test
---
.../postgres_fdw/expected/postgres_fdw.out | 54 +++++++++++++++++++
contrib/postgres_fdw/sql/postgres_fdw.sql | 53 ++++++++++++++++++
2 files changed, 107 insertions(+)
diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 2350cfe148..28b5af8d78 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -11798,3 +11798,57 @@ ANALYZE analyze_table;
-- cleanup
DROP FOREIGN TABLE analyze_ftable;
DROP TABLE analyze_table;
+-- ===================================================================
+-- test for postgres_fdw_verify_foreign_servers function
+-- ===================================================================
+-- Disable debug_discard_caches in order to manage remote connections
+SET debug_discard_caches TO '0';
+-- -- The text of the error might vary across platforms, so only show SQLSTATE.
+\set VERBOSITY sqlstate
+-- Disconnect once and set application_name to an arbitrary value
+SELECT 1 FROM postgres_fdw_disconnect_all();
+ ?column?
+----------
+ 1
+(1 row)
+
+ALTER SERVER loopback OPTIONS (SET application_name 'healthcheck');
+DO $$
+DECLARE
+ can_verify boolean;
+ result boolean;
+BEGIN
+ PERFORM 1 FROM ft1 LIMIT 1;
+
+ -- Terminate the remote backend process
+ PERFORM pg_terminate_backend(pid, 180000) FROM pg_stat_activity
+ WHERE application_name = 'healthcheck';
+
+ -- Check whether we can do health check on this platform
+ SELECT INTO can_verify postgres_fdw_can_verify_connection_states();
+
+ -- If the checking can be done on this platform, call it
+ IF can_verify IS TRUE THEN
+ -- Set client_min_messages to ERROR temporary because the following
+ -- function only throws a WARNING on the supported platform.
+ SET LOCAL client_min_messages TO ERROR;
+
+ SELECT INTO result postgres_fdw_verify_connection_states('loopback');
+
+ RESET client_min_messages;
+ ELSE
+ result = false;
+ END IF;
+
+ -- If result is FALSE, we succeeded to detect the disconnection or it could
+ -- not be done on this platform. Raise an message.
+ IF result IS FALSE THEN
+ RAISE INFO 'postgres_fdw_verify_connection_states() could detect the disconnection, or health check cannot be used on this platform';
+ END IF;
+END;
+$$;
+INFO: 00000
+ERROR: 08006
+-- Clean up
+\set VERBOSITY default
+RESET debug_discard_caches;
diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index c37aa80383..49042eb8c1 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -3974,3 +3974,56 @@ ANALYZE analyze_table;
-- cleanup
DROP FOREIGN TABLE analyze_ftable;
DROP TABLE analyze_table;
+
+-- ===================================================================
+-- test for postgres_fdw_verify_foreign_servers function
+-- ===================================================================
+
+-- Disable debug_discard_caches in order to manage remote connections
+SET debug_discard_caches TO '0';
+
+-- -- The text of the error might vary across platforms, so only show SQLSTATE.
+\set VERBOSITY sqlstate
+
+-- Disconnect once and set application_name to an arbitrary value
+SELECT 1 FROM postgres_fdw_disconnect_all();
+ALTER SERVER loopback OPTIONS (SET application_name 'healthcheck');
+
+DO $$
+DECLARE
+ can_verify boolean;
+ result boolean;
+BEGIN
+ PERFORM 1 FROM ft1 LIMIT 1;
+
+ -- Terminate the remote backend process
+ PERFORM pg_terminate_backend(pid, 180000) FROM pg_stat_activity
+ WHERE application_name = 'healthcheck';
+
+ -- Check whether we can do health check on this platform
+ SELECT INTO can_verify postgres_fdw_can_verify_connection_states();
+
+ -- If the checking can be done on this platform, call it
+ IF can_verify IS TRUE THEN
+ -- Set client_min_messages to ERROR temporary because the following
+ -- function only throws a WARNING on the supported platform.
+ SET LOCAL client_min_messages TO ERROR;
+
+ SELECT INTO result postgres_fdw_verify_connection_states('loopback');
+
+ RESET client_min_messages;
+ ELSE
+ result = false;
+ END IF;
+
+ -- If result is FALSE, we succeeded to detect the disconnection or it could
+ -- not be done on this platform. Raise an message.
+ IF result IS FALSE THEN
+ RAISE INFO 'postgres_fdw_verify_connection_states() could detect the disconnection, or health check cannot be used on this platform';
+ END IF;
+END;
+$$;
+
+-- Clean up
+\set VERBOSITY default
+RESET debug_discard_caches;
--
2.27.0
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Subject: RE: [Proposal] Add foreign-server health checks infrastructure
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