Make varcache dynamically configurable. (#867)

This change enables caching other postgres parameters in addition to the static list `{"client_encoding", "DateStyle", "TimeZone", "standard_conforming_strings", "application_name"}` that is already supported.

This also starts tracking IntervalStyle using this new mechanism by default.
 
Related to #452 and #482
Fixes #470
Fixes #821

.gitmodules

@@ -1,3 +1,6 @@
 [submodule "lib"]
 	path = lib
 	url = https://github.com/libusual/libusual.git
+[submodule "uthash"]
+	path = uthash
+	url = https://github.com/troydhanson/uthash.git

Makefile

@@ -59,7 +59,9 @@ pgbouncer_SOURCES = \
 	include/common/unicode_norm.h \
 	include/common/unicode_norm_table.h
 
+UTHASH = uthash
 pgbouncer_CPPFLAGS = -Iinclude $(CARES_CFLAGS) $(LIBEVENT_CFLAGS) $(TLS_CPPFLAGS)
+pgbouncer_CPPFLAGS += -I$(UTHASH)/src
 
 # include libusual sources directly
 AM_FEATURES = libusual
@@ -84,7 +86,8 @@ EXTRA_DIST = AUTHORS COPYRIGHT Makefile config.mak.in config.sub config.guess \
 	     install-sh autogen.sh configure configure.ac \
 	     etc/mkauth.py etc/optscan.sh etc/example.debian.init.sh \
 	     win32/Makefile \
-	     $(LIBUSUAL_DIST)
+	     $(LIBUSUAL_DIST) \
+	     $(UTHASH_DIST) \
 
 # libusual files (FIXME: list should be provided by libusual...)
 LIBUSUAL_DIST = $(filter-out %/config.h, $(sort $(wildcard \
@@ -98,6 +101,9 @@ LIBUSUAL_DIST = $(filter-out %/config.h, $(sort $(wildcard \
 		lib/README lib/COPYRIGHT \
 		lib/find_modules.sh )))
 
+UTHASH_DIST = $(UTHASH)/src/uthash.h \
+              $(UTHASH)/LICENSE
+
 pgbouncer_LDFLAGS := $(TLS_LDFLAGS)
 pgbouncer_LDADD := $(CARES_LIBS) $(LIBEVENT_LIBS) $(TLS_LIBS) $(LIBS)
 LIBS :=

doc/config.md

@@ -200,6 +200,25 @@ achieving uniform load.
 
 Default: 0
 
+### track_extra_parameters
+
+By default, PgBouncer tracks `client_encoding`, `datestyle`, `timezone`, `standard_conforming_strings`
+and `application_name` parameters per client. To allow other parameters to be tracked, they can be
+specified here, so that PgBouncer knows that they should be maintained in the client variable cache
+and restored in the server whenever the client becomes active.
+
+If you need to specify multiple values, use a comma-separated list (e.g.
+`default_transaction_readonly, IntervalStyle`)
+
+Note: Most parameters cannot be tracked this way. The only parameters that can be tracked are ones that
+Postgres reports to the client. Postgres has
+[an official list of parameters that it reports to the client](https://www.postgresql.org/docs/15/protocol-flow.html#PROTOCOL-ASYNC).
+Postgres extensions can change this list though, they can add parameters themselves that they also report,
+and they can start reporting already existing paremeters that Postgres does not report.
+Notably Citus 12.0+ causes Postgres to also report `search_path`.
+
+Default: IntervalStyle
+
 ### ignore_startup_parameters
 
 By default, PgBouncer allows only parameters it can keep track of in startup

etc/pgbouncer.ini

@@ -161,6 +161,11 @@ auth_file = /etc/pgbouncer/userlist.txt
 ;; is off, server_reset_query is used only for session-pooling.
 ;server_reset_query_always = 0
 
+;; Comma-separated list of parameters to track per client. The Postgres 
+;; parameters listed here will be cached per client by pgbouncer and 
+;; restored in server everytime the client runs a query. 
+;track_extra_parameters = IntervalStyle
+;
 ;; Comma-separated list of parameters to ignore when given in startup
 ;; packet.  Newer JDBC versions require the extra_float_digits here.
 ;ignore_startup_parameters = extra_float_digits

include/objects.h

@@ -32,6 +32,7 @@ extern struct Slab *peer_pool_cache;
 extern struct Slab *pool_cache;
 extern struct Slab *user_cache;
 extern struct Slab *iobuf_cache;
+extern struct Slab *var_list_cache;
 
 PgDatabase *find_peer(int peer_id);
 PgDatabase *find_database(const char *name);

include/varcache.h

@@ -12,9 +12,11 @@ enum VarCacheIdx {
 typedef struct VarCache VarCache;
 
 struct VarCache {
-	struct PStr *var_list[NumVars];
+	struct PStr **var_list;
 };
 
+void init_var_lookup(const char *cf_track_extra_parameters);
+int get_num_var_cached(void);
 bool varcache_set(VarCache *cache, const char *key, const char *value) /* _MUSTCHECK */;
 bool varcache_apply(PgSocket *server, PgSocket *client, bool *changes_p) _MUSTCHECK;
 void varcache_fill_unset(VarCache *src, PgSocket *dst);

src/janitor.c

@@ -761,6 +761,7 @@ void kill_pool(PgPool *pool)
 	list_del(&pool->map_head);
 	statlist_remove(&pool_list, &pool->head);
 	varcache_clean(&pool->orig_vars);
+	slab_free(var_list_cache, pool->orig_vars.var_list);
 	slab_free(pool_cache, pool);
 }
 
@@ -778,6 +779,7 @@ void kill_peer_pool(PgPool *pool)
 	list_del(&pool->map_head);
 	statlist_remove(&peer_pool_list, &pool->head);
 	varcache_clean(&pool->orig_vars);
+	slab_free(var_list_cache, pool->orig_vars.var_list);
 	slab_free(peer_pool_cache, pool);
 }
 

src/main.c

@@ -116,6 +116,7 @@ char *cf_auth_hba_file;
 char *cf_auth_user;
 char *cf_auth_query;
 char *cf_auth_dbname;
+char *cf_track_extra_parameters;
 
 int cf_max_client_conn;
 int cf_default_pool_size;
@@ -314,6 +315,7 @@ CF_ABS("tcp_keepidle", CF_INT, cf_tcp_keepidle, 0, "0"),
 CF_ABS("tcp_keepintvl", CF_INT, cf_tcp_keepintvl, 0, "0"),
 CF_ABS("tcp_socket_buffer", CF_INT, cf_tcp_socket_buffer, 0, "0"),
 CF_ABS("tcp_user_timeout", CF_INT, cf_tcp_user_timeout, 0, "0"),
+CF_ABS("track_extra_parameters", CF_STR, cf_track_extra_parameters, CF_NO_RELOAD, "IntervalStyle"),
 CF_ABS("unix_socket_dir", CF_STR, cf_unix_socket_dir, CF_NO_RELOAD, DEFAULT_UNIX_SOCKET_DIR),
 #ifndef WIN32
 CF_ABS("unix_socket_group", CF_STR, cf_unix_socket_group, CF_NO_RELOAD, ""),
@@ -893,6 +895,8 @@ static void cleanup(void)
 	xfree((char **)&cf_logfile);
 	xfree((char **)&cf_syslog_ident);
 	xfree((char **)&cf_syslog_facility);
+
+	xfree(&cf_track_extra_parameters);
 }
 
 /* boot everything */
@@ -973,6 +977,7 @@ int main(int argc, char *argv[])
 	init_objects();
 	load_config();
 	main_config.loaded = true;
+	init_var_lookup(cf_track_extra_parameters);
 	init_caches();
 	logging_prefix_cb = log_socket_prefix;
 

src/objects.c

@@ -60,6 +60,7 @@ struct Slab *peer_pool_cache;
 struct Slab *pool_cache;
 struct Slab *user_cache;
 struct Slab *iobuf_cache;
+struct Slab *var_list_cache;
 
 /*
  * libevent may still report events when event_del()
@@ -91,6 +92,7 @@ static void construct_client(void *obj)
 	memset(client, 0, sizeof(PgSocket));
 	list_init(&client->head);
 	sbuf_init(&client->sbuf, client_proto);
+	client->vars.var_list = slab_alloc(var_list_cache);
 	client->state = CL_FREE;
 }
 
@@ -101,6 +103,7 @@ static void construct_server(void *obj)
 	memset(server, 0, sizeof(PgSocket));
 	list_init(&server->head);
 	sbuf_init(&server->sbuf, server_proto);
+	server->vars.var_list = slab_alloc(var_list_cache);
 	server->state = SV_FREE;
 }
 
@@ -146,6 +149,7 @@ void init_caches(void)
 	server_cache = slab_create("server_cache", sizeof(PgSocket), 0, construct_server, USUAL_ALLOC);
 	client_cache = slab_create("client_cache", sizeof(PgSocket), 0, construct_client, USUAL_ALLOC);
 	iobuf_cache = slab_create("iobuf_cache", IOBUF_SIZE, 0, do_iobuf_reset, USUAL_ALLOC);
+	var_list_cache = slab_create("var_list_cache", sizeof(struct PStr*) * get_num_var_cached(), 0, NULL, USUAL_ALLOC);
 }
 
 /* state change means moving between lists */
@@ -191,6 +195,7 @@ void change_client_state(PgSocket *client, SocketState newstate)
 	switch (client->state) {
 	case CL_FREE:
 		varcache_clean(&client->vars);
+		slab_free(var_list_cache, client->vars.var_list);
 		slab_free(client_cache, client);
 		break;
 	case CL_JUSTFREE:
@@ -261,6 +266,7 @@ void change_server_state(PgSocket *server, SocketState newstate)
 	switch (server->state) {
 	case SV_FREE:
 		varcache_clean(&server->vars);
+		slab_free(var_list_cache, server->vars.var_list);
 		slab_free(server_cache, server);
 		break;
 	case SV_JUSTFREE:
@@ -583,6 +589,7 @@ static PgPool *new_pool(PgDatabase *db, PgUser *user)
 
 	list_init(&pool->head);
 	list_init(&pool->map_head);
+	pool->orig_vars.var_list = slab_alloc(var_list_cache);
 
 	pool->user = user;
 	pool->db = db;
@@ -625,6 +632,7 @@ static PgPool *new_peer_pool(PgDatabase *db)
 
 	list_init(&pool->head);
 	list_init(&pool->map_head);
+	pool->orig_vars.var_list = slab_alloc(var_list_cache);
 
 	pool->db = db;
 
@@ -2242,4 +2250,6 @@ void objects_cleanup(void)
 	user_cache = NULL;
 	slab_destroy(iobuf_cache);
 	iobuf_cache = NULL;
+	slab_destroy(var_list_cache);
+	var_list_cache = NULL;
 }