X-Git-Url: https://git.octo.it/?a=blobdiff_plain;f=src%2Fpostgresql.c;h=1eaf6bd3877570a56c0e50c045b7e90cc888cda2;hb=33fdd7d22e7e122c337b0092d3c8d26e5f3caa70;hp=faad16cd9b02b404c5326279bd8fa1aa85e64624;hpb=68ab7da7a51018a00e6e03347182b988a30296a7;p=collectd.git

diff --git a/src/postgresql.c b/src/postgresql.c
index faad16cd..1eaf6bd3 100644
--- a/src/postgresql.c
+++ b/src/postgresql.c
@@ -1,22 +1,35 @@
 /**
  * collectd - src/postgresql.c
- * Copyright (C) 2008  Sebastian Harl
+ * Copyright (C) 2008-2012  Sebastian Harl
+ * Copyright (C) 2009       Florian Forster
+ * All rights reserved.
  *
- * This program is free software; you can redistribute it and/or modify it
- * under the terms of the GNU General Public License as published by the
- * Free Software Foundation; only version 2 of the License is applicable.
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
  *
- * This program is distributed in the hope that it will be useful, but
- * WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
- * General Public License for more details.
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
  *
- * You should have received a copy of the GNU General Public License along
- * with this program; if not, write to the Free Software Foundation, Inc.,
- * 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
+ * - Redistributions in binary form must reproduce the above copyright
+ *   notice, this list of conditions and the following disclaimer in the
+ *   documentation and/or other materials provided with the distribution.
  *
- * Author:
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ * Authors:
  *   Sebastian Harl <sh at tokkee.org>
+ *   Florian Forster <octo at verplant.org>
  **/
 
 /*
@@ -29,14 +42,21 @@
 #include "configfile.h"
 #include "plugin.h"
 
+#include "utils_cache.h"
+#include "utils_db_query.h"
 #include "utils_complain.h"
 
+#if HAVE_PTHREAD_H
+# include <pthread.h>
+#endif
+
 #include <pg_config_manual.h>
 #include <libpq-fe.h>
 
 #define log_err(...) ERROR ("postgresql: " __VA_ARGS__)
 #define log_warn(...) WARNING ("postgresql: " __VA_ARGS__)
 #define log_info(...) INFO ("postgresql: " __VA_ARGS__)
+#define log_debug(...) DEBUG ("postgresql: " __VA_ARGS__)
 
 #ifndef C_PSQL_DEFAULT_CONF
 # define C_PSQL_DEFAULT_CONF PKGDATADIR "/postgresql_default.conf"
@@ -80,39 +100,47 @@ typedef enum {
 	C_PSQL_PARAM_HOST = 1,
 	C_PSQL_PARAM_DB,
 	C_PSQL_PARAM_USER,
+	C_PSQL_PARAM_INTERVAL,
+	C_PSQL_PARAM_INSTANCE,
 } c_psql_param_t;
 
+/* Parameter configuration. Stored as `user data' in the query objects. */
 typedef struct {
-	char *type;
-	char *type_instance;
-	int   ds_type;
-} c_psql_col_t;
-
-typedef struct {
-	char *name;
-	char *query;
-
 	c_psql_param_t *params;
 	int             params_num;
+} c_psql_user_data_t;
 
-	c_psql_col_t *cols;
-	int           cols_num;
-
-	int min_pg_version;
-	int max_pg_version;
-} c_psql_query_t;
+typedef struct {
+	char *name;
+	char *statement;
+	_Bool store_rates;
+} c_psql_writer_t;
 
 typedef struct {
 	PGconn      *conn;
 	c_complain_t conn_complaint;
 
 	int proto_version;
+	int server_version;
 
 	int max_params_num;
 
 	/* user configuration */
-	c_psql_query_t **queries;
-	int              queries_num;
+	udb_query_preparation_area_t **q_prep_areas;
+	udb_query_t    **queries;
+	size_t           queries_num;
+
+	c_psql_writer_t **writers;
+	size_t            writers_num;
+
+	/* make sure we don't access the database object in parallel */
+	pthread_mutex_t   db_lock;
+
+	cdtime_t interval;
+
+	/* writer "caching" settings */
+	cdtime_t commit_interval;
+	cdtime_t next_commit;
 
 	char *host;
 	char *port;
@@ -120,11 +148,15 @@ typedef struct {
 	char *user;
 	char *password;
 
+	char *instance;
+
 	char *sslmode;
 
 	char *krbsrvname;
 
 	char *service;
+
+	int ref_cnt;
 } c_psql_database_t;
 
 static char *def_queries[] = {
@@ -138,94 +170,99 @@ static char *def_queries[] = {
 };
 static int def_queries_num = STATIC_ARRAY_SIZE (def_queries);
 
-static c_psql_query_t *queries          = NULL;
-static int             queries_num      = 0;
-
-static c_psql_database_t *databases     = NULL;
-static int                databases_num = 0;
-
-static c_psql_query_t *c_psql_query_new (const char *name)
-{
-	c_psql_query_t *query;
-
-	++queries_num;
-	if (NULL == (queries = (c_psql_query_t *)realloc (queries,
-				queries_num * sizeof (*queries)))) {
-		log_err ("Out of memory.");
-		exit (5);
-	}
-	query = queries + queries_num - 1;
+static c_psql_database_t **databases     = NULL;
+static size_t              databases_num = 0;
 
-	query->name  = sstrdup (name);
-	query->query = NULL;
+static udb_query_t       **queries       = NULL;
+static size_t              queries_num   = 0;
 
-	query->params     = NULL;
-	query->params_num = 0;
+static c_psql_writer_t    *writers       = NULL;
+static size_t              writers_num   = 0;
 
-	query->cols     = NULL;
-	query->cols_num = 0;
-
-	query->min_pg_version = 0;
-	query->max_pg_version = INT_MAX;
-	return query;
-} /* c_psql_query_new */
-
-static void c_psql_query_delete (c_psql_query_t *query)
+static int c_psql_begin (c_psql_database_t *db)
 {
-	int i;
+	PGresult *r = PQexec (db->conn, "BEGIN");
 
-	sfree (query->name);
-	sfree (query->query);
+	int status = 1;
 
-	sfree (query->params);
-	query->params_num = 0;
-
-	for (i = 0; i < query->cols_num; ++i) {
-		sfree (query->cols[i].type);
-		sfree (query->cols[i].type_instance);
+	if (r != NULL) {
+		if (PGRES_COMMAND_OK == PQresultStatus (r)) {
+			db->next_commit = cdtime() + db->commit_interval;
+			status = 0;
+		}
+		else
+			log_warn ("Failed to initiate ('BEGIN') transaction: %s",
+					PQerrorMessage (db->conn));
+		PQclear (r);
 	}
-	sfree (query->cols);
-	query->cols_num = 0;
-	return;
-} /* c_psql_query_delete */
+	return status;
+} /* c_psql_begin */
 
-static c_psql_query_t *c_psql_query_get (const char *name, int server_version)
+static int c_psql_commit (c_psql_database_t *db)
 {
-	int i;
+	PGresult *r = PQexec (db->conn, "COMMIT");
 
-	for (i = 0; i < queries_num; ++i)
-		if (0 == strcasecmp (name, queries[i].name)
-				&& ((-1 == server_version)
-					|| ((queries[i].min_pg_version <= server_version)
-						&& (server_version <= queries[i].max_pg_version))))
-			return queries + i;
-	return NULL;
-} /* c_psql_query_get */
+	int status = 1;
+
+	if (r != NULL) {
+		if (PGRES_COMMAND_OK == PQresultStatus (r)) {
+			db->next_commit = 0;
+			log_debug ("Successfully committed transaction.");
+			status = 0;
+		}
+		else
+			log_warn ("Failed to commit transaction: %s",
+					PQerrorMessage (db->conn));
+		PQclear (r);
+	}
+	return status;
+} /* c_psql_commit */
 
 static c_psql_database_t *c_psql_database_new (const char *name)
 {
-	c_psql_database_t *db;
+	c_psql_database_t **tmp;
+	c_psql_database_t  *db;
 
-	++databases_num;
-	if (NULL == (databases = (c_psql_database_t *)realloc (databases,
-				databases_num * sizeof (*databases)))) {
+	db = (c_psql_database_t *)malloc (sizeof(*db));
+	if (NULL == db) {
+		log_err ("Out of memory.");
+		return NULL;
+	}
+
+	tmp = (c_psql_database_t **)realloc (databases,
+			(databases_num + 1) * sizeof (*databases));
+	if (NULL == tmp) {
 		log_err ("Out of memory.");
-		exit (5);
+		sfree (db);
+		return NULL;
 	}
 
-	db = databases + (databases_num - 1);
+	databases = tmp;
+	databases[databases_num] = db;
+	++databases_num;
 
 	db->conn = NULL;
 
-	db->conn_complaint.last     = 0;
-	db->conn_complaint.interval = 0;
+	C_COMPLAIN_INIT (&db->conn_complaint);
 
 	db->proto_version = 0;
+	db->server_version = 0;
 
 	db->max_params_num = 0;
 
-	db->queries     = NULL;
-	db->queries_num = 0;
+	db->q_prep_areas   = NULL;
+	db->queries        = NULL;
+	db->queries_num    = 0;
+
+	db->writers        = NULL;
+	db->writers_num    = 0;
+
+	pthread_mutex_init (&db->db_lock, /* attrs = */ NULL);
+
+	db->interval   = 0;
+
+	db->commit_interval = 0;
+	db->next_commit     = 0;
 
 	db->database   = sstrdup (name);
 	db->host       = NULL;
@@ -233,96 +270,116 @@ static c_psql_database_t *c_psql_database_new (const char *name)
 	db->user       = NULL;
 	db->password   = NULL;
 
+	db->instance   = sstrdup (name);
+
 	db->sslmode    = NULL;
 
 	db->krbsrvname = NULL;
 
 	db->service    = NULL;
+
+	db->ref_cnt    = 0;
 	return db;
 } /* c_psql_database_new */
 
-static void c_psql_database_delete (c_psql_database_t *db)
+static void c_psql_database_delete (void *data)
 {
+	size_t i;
+
+	c_psql_database_t *db = data;
+
+	--db->ref_cnt;
+	/* readers and writers may access this database */
+	if (db->ref_cnt > 0)
+		return;
+
+	/* wait for the lock to be released by the last writer */
+	pthread_mutex_lock (&db->db_lock);
+
+	if (db->next_commit > 0)
+		c_psql_commit (db);
+
 	PQfinish (db->conn);
 	db->conn = NULL;
 
+	if (db->q_prep_areas)
+		for (i = 0; i < db->queries_num; ++i)
+			udb_query_delete_preparation_area (db->q_prep_areas[i]);
+	free (db->q_prep_areas);
+
 	sfree (db->queries);
 	db->queries_num = 0;
 
+	sfree (db->writers);
+	db->writers_num = 0;
+
+	pthread_mutex_unlock (&db->db_lock);
+
+	pthread_mutex_destroy (&db->db_lock);
+
 	sfree (db->database);
 	sfree (db->host);
 	sfree (db->port);
 	sfree (db->user);
 	sfree (db->password);
 
+	sfree (db->instance);
+
 	sfree (db->sslmode);
 
 	sfree (db->krbsrvname);
 
 	sfree (db->service);
+
+	/* don't care about freeing or reordering the 'databases' array
+	 * this is done in 'shutdown'; also, don't free the database instance
+	 * object just to make sure that in case anybody accesses it before
+	 * shutdown won't segfault */
 	return;
 } /* c_psql_database_delete */
 
-static void submit (const c_psql_database_t *db,
-		const char *type, const char *type_instance,
-		value_t *values, size_t values_len)
+static int c_psql_connect (c_psql_database_t *db)
 {
-	value_list_t vl = VALUE_LIST_INIT;
-
-	vl.values     = values;
-	vl.values_len = values_len;
-	vl.time       = time (NULL);
-
-	if (C_PSQL_IS_UNIX_DOMAIN_SOCKET (db->host)
-			|| (0 == strcmp (db->host, "localhost")))
-		sstrncpy (vl.host, hostname_g, sizeof (vl.host));
-	else
-		sstrncpy (vl.host, db->host, sizeof (vl.host));
+	char  conninfo[4096];
+	char *buf     = conninfo;
+	int   buf_len = sizeof (conninfo);
+	int   status;
 
-	sstrncpy (vl.plugin, "postgresql", sizeof (vl.plugin));
-	sstrncpy (vl.plugin_instance, db->database, sizeof (vl.plugin_instance));
+	if ((! db) || (! db->database))
+		return -1;
 
-	sstrncpy (vl.type, type, sizeof (vl.type));
+	status = ssnprintf (buf, buf_len, "dbname = '%s'", db->database);
+	if (0 < status) {
+		buf     += status;
+		buf_len -= status;
+	}
 
-	if (NULL != type_instance)
-		sstrncpy (vl.type_instance, type_instance, sizeof (vl.type_instance));
+	C_PSQL_PAR_APPEND (buf, buf_len, "host",       db->host);
+	C_PSQL_PAR_APPEND (buf, buf_len, "port",       db->port);
+	C_PSQL_PAR_APPEND (buf, buf_len, "user",       db->user);
+	C_PSQL_PAR_APPEND (buf, buf_len, "password",   db->password);
+	C_PSQL_PAR_APPEND (buf, buf_len, "sslmode",    db->sslmode);
+	C_PSQL_PAR_APPEND (buf, buf_len, "krbsrvname", db->krbsrvname);
+	C_PSQL_PAR_APPEND (buf, buf_len, "service",    db->service);
 
-	plugin_dispatch_values (&vl);
-	return;
-} /* submit */
+	db->conn = PQconnectdb (conninfo);
+	db->proto_version = PQprotocolVersion (db->conn);
+	return 0;
+} /* c_psql_connect */
 
-static void submit_counter (const c_psql_database_t *db,
-		const char *type, const char *type_instance,
-		const char *value)
+static int c_psql_check_connection (c_psql_database_t *db)
 {
-	value_t values[1];
+	_Bool init = 0;
 
-	if ((NULL == value) || ('\0' == *value))
-		return;
+	if (! db->conn) {
+		init = 1;
 
-	values[0].counter = atoll (value);
-	submit (db, type, type_instance, values, 1);
-	return;
-} /* submit_counter */
-
-static void submit_gauge (const c_psql_database_t *db,
-		const char *type, const char *type_instance,
-		const char *value)
-{
-	value_t values[1];
-
-	if ((NULL == value) || ('\0' == *value))
-		return;
-
-	values[0].gauge = atof (value);
-	submit (db, type, type_instance, values, 1);
-	return;
-} /* submit_gauge */
+		/* trigger c_release() */
+		if (0 == db->conn_complaint.interval)
+			db->conn_complaint.interval = 1;
 
-static int c_psql_check_connection (c_psql_database_t *db)
-{
-	/* "ping" */
-	PQclear (PQexec (db->conn, "SELECT 42;"));
+		c_psql_connect (db);
+	}
 
 	if (CONNECTION_OK != PQstatus (db->conn)) {
 		PQreset (db->conn);
@@ -333,32 +390,60 @@ static int c_psql_check_connection (c_psql_database_t *db)
 
 		if (CONNECTION_OK != PQstatus (db->conn)) {
 			c_complain (LOG_ERR, &db->conn_complaint,
-					"Failed to connect to database %s: %s",
-					db->database, PQerrorMessage (db->conn));
+					"Failed to connect to database %s (%s): %s",
+					db->database, db->instance,
+					PQerrorMessage (db->conn));
 			return -1;
 		}
 
 		db->proto_version = PQprotocolVersion (db->conn);
+	}
+
+	db->server_version = PQserverVersion (db->conn);
+
+	if (c_would_release (&db->conn_complaint)) {
+		char *server_host;
+		int   server_version;
+
+		server_host    = PQhost (db->conn);
+		server_version = PQserverVersion (db->conn);
+
+		c_do_release (LOG_INFO, &db->conn_complaint,
+				"Successfully %sconnected to database %s (user %s) "
+				"at server %s%s%s (server version: %d.%d.%d, "
+				"protocol version: %d, pid: %d)", init ? "" : "re",
+				PQdb (db->conn), PQuser (db->conn),
+				C_PSQL_SOCKET3 (server_host, PQport (db->conn)),
+				C_PSQL_SERVER_VERSION3 (server_version),
+				db->proto_version, PQbackendPID (db->conn));
+
 		if (3 > db->proto_version)
 			log_warn ("Protocol version %d does not support parameters.",
 					db->proto_version);
 	}
-
-	c_release (LOG_INFO, &db->conn_complaint,
-			"Successfully reconnected to database %s", PQdb (db->conn));
 	return 0;
 } /* c_psql_check_connection */
 
+static PGresult *c_psql_exec_query_noparams (c_psql_database_t *db,
+		udb_query_t *q)
+{
+	return PQexec (db->conn, udb_query_get_statement (q));
+} /* c_psql_exec_query_noparams */
+
 static PGresult *c_psql_exec_query_params (c_psql_database_t *db,
-		c_psql_query_t *query)
+		udb_query_t *q, c_psql_user_data_t *data)
 {
 	char *params[db->max_params_num];
+	char  interval[64];
 	int   i;
 
-	assert (db->max_params_num >= query->params_num);
+	if ((data == NULL) || (data->params_num == 0))
+		return (c_psql_exec_query_noparams (db, q));
+
+	assert (db->max_params_num >= data->params_num);
 
-	for (i = 0; i < query->params_num; ++i) {
-		switch (query->params[i]) {
+	for (i = 0; i < data->params_num; ++i) {
+		switch (data->params[i]) {
 			case C_PSQL_PARAM_HOST:
 				params[i] = C_PSQL_IS_UNIX_DOMAIN_SOCKET (db->host)
 					? "localhost" : db->host;
@@ -369,458 +454,750 @@ static PGresult *c_psql_exec_query_params (c_psql_database_t *db,
 			case C_PSQL_PARAM_USER:
 				params[i] = db->user;
 				break;
+			case C_PSQL_PARAM_INTERVAL:
+				ssnprintf (interval, sizeof (interval), "%.3f",
+						(db->interval > 0)
+						? CDTIME_T_TO_DOUBLE (db->interval)
+						: plugin_get_interval ());
+				params[i] = interval;
+				break;
+			case C_PSQL_PARAM_INSTANCE:
+				params[i] = db->instance;
+				break;
 			default:
 				assert (0);
 		}
 	}
 
-	return PQexecParams (db->conn, query->query, query->params_num, NULL,
-			(const char *const *)((0 == query->params_num) ? NULL : params),
+	return PQexecParams (db->conn, udb_query_get_statement (q),
+			data->params_num, NULL,
+			(const char *const *) params,
 			NULL, NULL, /* return text data */ 0);
 } /* c_psql_exec_query_params */
 
-static PGresult *c_psql_exec_query_noparams (c_psql_database_t *db,
-		c_psql_query_t *query)
+/* db->db_lock must be locked when calling this function */
+static int c_psql_exec_query (c_psql_database_t *db, udb_query_t *q,
+		udb_query_preparation_area_t *prep_area)
 {
-	return PQexec (db->conn, query->query);
-} /* c_psql_exec_query_noparams */
+	PGresult *res;
 
-static int c_psql_exec_query (c_psql_database_t *db, int idx)
-{
-	c_psql_query_t *query;
-	PGresult       *res;
+	c_psql_user_data_t *data;
 
-	int rows, cols;
-	int i;
+	const char *host;
 
-	if (idx >= db->queries_num)
-		return -1;
+	char **column_names;
+	char **column_values;
+	int    column_num;
+
+	int rows_num;
+	int status;
+	int row, col;
 
-	query = db->queries[idx];
+	/* The user data may hold parameter information, but may be NULL. */
+	data = udb_query_get_user_data (q);
 
+	/* Versions up to `3' don't know how to handle parameters. */
 	if (3 <= db->proto_version)
-		res = c_psql_exec_query_params (db, query);
-	else if (0 == query->params_num)
-		res = c_psql_exec_query_noparams (db, query);
+		res = c_psql_exec_query_params (db, q, data);
+	else if ((NULL == data) || (0 == data->params_num))
+		res = c_psql_exec_query_noparams (db, q);
 	else {
-		log_err ("Connection to database \"%s\" does not support parameters "
-				"(protocol version %d) - cannot execute query \"%s\".",
-				db->database, db->proto_version, query->name);
+		log_err ("Connection to database \"%s\" (%s) does not support "
+				"parameters (protocol version %d) - "
+				"cannot execute query \"%s\".",
+				db->database, db->instance, db->proto_version,
+				udb_query_get_name (q));
 		return -1;
 	}
 
+	/* give c_psql_write() a chance to acquire the lock if called recursively
+	 * through dispatch_values(); this will happen if, both, queries and
+	 * writers are configured for a single connection */
+	pthread_mutex_unlock (&db->db_lock);
+
+	column_names = NULL;
+	column_values = NULL;
+
 	if (PGRES_TUPLES_OK != PQresultStatus (res)) {
+		pthread_mutex_lock (&db->db_lock);
+
+		if ((CONNECTION_OK != PQstatus (db->conn))
+				&& (0 == c_psql_check_connection (db))) {
+			PQclear (res);
+			return c_psql_exec_query (db, q, prep_area);
+		}
+
 		log_err ("Failed to execute SQL query: %s",
 				PQerrorMessage (db->conn));
-		log_info ("SQL query was: %s", query->query);
+		log_info ("SQL query was: %s",
+				udb_query_get_statement (q));
 		PQclear (res);
 		return -1;
 	}
 
-	rows = PQntuples (res);
-	if (1 > rows) {
-		PQclear (res);
-		return 0;
+#define BAIL_OUT(status) \
+	sfree (column_names); \
+	sfree (column_values); \
+	PQclear (res); \
+	pthread_mutex_lock (&db->db_lock); \
+	return status
+
+	rows_num = PQntuples (res);
+	if (1 > rows_num) {
+		BAIL_OUT (0);
 	}
 
-	cols = PQnfields (res);
-	if (query->cols_num != cols) {
-		log_err ("SQL query returned wrong number of fields "
-				"(expected: %i, got: %i)", query->cols_num, cols);
-		log_info ("SQL query was: %s", query->query);
-		PQclear (res);
-		return -1;
+	column_num = PQnfields (res);
+	column_names = (char **) calloc (column_num, sizeof (char *));
+	if (NULL == column_names) {
+		log_err ("calloc failed.");
+		BAIL_OUT (-1);
 	}
 
-	for (i = 0; i < rows; ++i) {
-		int j;
+	column_values = (char **) calloc (column_num, sizeof (char *));
+	if (NULL == column_values) {
+		log_err ("calloc failed.");
+		BAIL_OUT (-1);
+	}
+	
+	for (col = 0; col < column_num; ++col) {
+		/* Pointers returned by `PQfname' are freed by `PQclear' via
+		 * `BAIL_OUT'. */
+		column_names[col] = PQfname (res, col);
+		if (NULL == column_names[col]) {
+			log_err ("Failed to resolve name of column %i.", col);
+			BAIL_OUT (-1);
+		}
+	}
 
-		for (j = 0; j < cols; ++j) {
-			c_psql_col_t col = query->cols[j];
+	if (C_PSQL_IS_UNIX_DOMAIN_SOCKET (db->host)
+			|| (0 == strcmp (db->host, "localhost")))
+		host = hostname_g;
+	else
+		host = db->host;
+
+	status = udb_query_prepare_result (q, prep_area, host, "postgresql",
+			db->instance, column_names, (size_t) column_num, db->interval);
+	if (0 != status) {
+		log_err ("udb_query_prepare_result failed with status %i.",
+				status);
+		BAIL_OUT (-1);
+	}
 
-			char *value = PQgetvalue (res, i, j);
+	for (row = 0; row < rows_num; ++row) {
+		for (col = 0; col < column_num; ++col) {
+			/* Pointers returned by `PQgetvalue' are freed by `PQclear' via
+			 * `BAIL_OUT'. */
+			column_values[col] = PQgetvalue (res, row, col);
+			if (NULL == column_values[col]) {
+				log_err ("Failed to get value at (row = %i, col = %i).",
+						row, col);
+				break;
+			}
+		}
 
-			if (col.ds_type == DS_TYPE_COUNTER)
-				submit_counter (db, col.type, col.type_instance, value);
-			else if (col.ds_type == DS_TYPE_GAUGE)
-				submit_gauge (db, col.type, col.type_instance, value);
+		/* check for an error */
+		if (col < column_num)
+			continue;
+
+		status = udb_query_handle_result (q, prep_area, column_values);
+		if (status != 0) {
+			log_err ("udb_query_handle_result failed with status %i.",
+					status);
 		}
-	}
-	PQclear (res);
-	return 0;
+	} /* for (row = 0; row < rows_num; ++row) */
+
+	udb_query_finish_result (q, prep_area);
+
+	BAIL_OUT (0);
+#undef BAIL_OUT
 } /* c_psql_exec_query */
 
-static int c_psql_read (void)
+static int c_psql_read (user_data_t *ud)
 {
+	c_psql_database_t *db;
+
 	int success = 0;
 	int i;
 
-	for (i = 0; i < databases_num; ++i) {
-		c_psql_database_t *db = databases + i;
+	if ((ud == NULL) || (ud->data == NULL)) {
+		log_err ("c_psql_read: Invalid user data.");
+		return -1;
+	}
 
-		int j;
+	db = ud->data;
 
-		assert (NULL != db->database);
+	assert (NULL != db->database);
+	assert (NULL != db->instance);
+	assert (NULL != db->queries);
 
-		if (0 != c_psql_check_connection (db))
-			continue;
+	pthread_mutex_lock (&db->db_lock);
+
+	if (0 != c_psql_check_connection (db)) {
+		pthread_mutex_unlock (&db->db_lock);
+		return -1;
+	}
+
+	for (i = 0; i < db->queries_num; ++i)
+	{
+		udb_query_preparation_area_t *prep_area;
+		udb_query_t *q;
 
-		for (j = 0; j < db->queries_num; ++j)
-			c_psql_exec_query (db, j);
+		prep_area = db->q_prep_areas[i];
+		q = db->queries[i];
+
+		if ((0 != db->server_version)
+				&& (udb_query_check_version (q, db->server_version) <= 0))
+			continue;
 
-		++success;
+		if (0 == c_psql_exec_query (db, q, prep_area))
+			success = 1;
 	}
 
+	pthread_mutex_unlock (&db->db_lock);
+
 	if (! success)
 		return -1;
 	return 0;
 } /* c_psql_read */
 
-static int c_psql_shutdown (void)
+static char *values_name_to_sqlarray (const data_set_t *ds,
+		char *string, size_t string_len)
 {
+	char  *str_ptr;
+	size_t str_len;
+
 	int i;
 
-	if ((NULL == databases) || (0 == databases_num))
-		return 0;
+	str_ptr = string;
+	str_len = string_len;
 
-	plugin_unregister_read ("postgresql");
-	plugin_unregister_shutdown ("postgresql");
+	for (i = 0; i < ds->ds_num; ++i) {
+		int status = ssnprintf (str_ptr, str_len, ",'%s'", ds->ds[i].name);
 
-	for (i = 0; i < databases_num; ++i) {
-		c_psql_database_t *db = databases + i;
-		c_psql_database_delete (db);
+		if (status < 1)
+			return NULL;
+		else if ((size_t)status >= str_len) {
+			str_len = 0;
+			break;
+		}
+		else {
+			str_ptr += status;
+			str_len -= (size_t)status;
+		}
 	}
 
-	sfree (databases);
-	databases_num = 0;
+	if (str_len <= 2) {
+		log_err ("c_psql_write: Failed to stringify value names");
+		return NULL;
+	}
+
+	/* overwrite the first comma */
+	string[0] = '{';
+	str_ptr[0] = '}';
+	str_ptr[1] = '\0';
+
+	return string;
+} /* values_name_to_sqlarray */
 
-	for (i = 0; i < queries_num; ++i) {
-		c_psql_query_t *query = queries + i;
-		c_psql_query_delete (query);
+static char *values_type_to_sqlarray (const data_set_t *ds,
+		char *string, size_t string_len, _Bool store_rates)
+{
+	char  *str_ptr;
+	size_t str_len;
+
+	int i;
+
+	str_ptr = string;
+	str_len = string_len;
+
+	for (i = 0; i < ds->ds_num; ++i) {
+		int status;
+
+		if (store_rates)
+			status = ssnprintf(str_ptr, str_len, ",'gauge'");
+		else
+			status = ssnprintf(str_ptr, str_len, ",'%s'",
+					DS_TYPE_TO_STRING (ds->ds[i].type));
+
+		if (status < 1) {
+			str_len = 0;
+			break;
+		}
+		else if ((size_t)status >= str_len) {
+			str_len = 0;
+			break;
+		}
+		else {
+			str_ptr += status;
+			str_len -= (size_t)status;
+		}
 	}
 
-	sfree (queries);
-	queries_num = 0;
-	return 0;
-} /* c_psql_shutdown */
+	if (str_len <= 2) {
+		log_err ("c_psql_write: Failed to stringify value types");
+		return NULL;
+	}
+
+	/* overwrite the first comma */
+	string[0] = '{';
+	str_ptr[0] = '}';
+	str_ptr[1] = '\0';
 
-static int c_psql_init (void)
+	return string;
+} /* values_type_to_sqlarray */
+
+static char *values_to_sqlarray (const data_set_t *ds, const value_list_t *vl,
+		char *string, size_t string_len, _Bool store_rates)
 {
+	char  *str_ptr;
+	size_t str_len;
+
+	gauge_t *rates = NULL;
+
 	int i;
 
-	if ((NULL == databases) || (0 == databases_num))
-		return 0;
+	str_ptr = string;
+	str_len = string_len;
 
-	for (i = 0; i < queries_num; ++i) {
-		c_psql_query_t *query = queries + i;
-		int j;
+	for (i = 0; i < vl->values_len; ++i) {
+		int status = 0;
 
-		for (j = 0; j < query->cols_num; ++j) {
-			c_psql_col_t     *col = query->cols + j;
-			const data_set_t *ds;
+		if ((ds->ds[i].type != DS_TYPE_GAUGE)
+				&& (ds->ds[i].type != DS_TYPE_COUNTER)
+				&& (ds->ds[i].type != DS_TYPE_DERIVE)
+				&& (ds->ds[i].type != DS_TYPE_ABSOLUTE)) {
+			log_err ("c_psql_write: Unknown data source type: %i",
+					ds->ds[i].type);
+			sfree (rates);
+			return NULL;
+		}
 
-			ds = plugin_get_ds (col->type);
-			if (NULL == ds) {
-				log_err ("Column: Unknown type \"%s\".", col->type);
-				c_psql_shutdown ();
-				return -1;
-			}
+		if (ds->ds[i].type == DS_TYPE_GAUGE)
+			status = ssnprintf (str_ptr, str_len,
+					",%f", vl->values[i].gauge);
+		else if (store_rates) {
+			if (rates == NULL)
+				rates = uc_get_rate (ds, vl);
 
-			if (1 != ds->ds_num) {
-				log_err ("Column: Invalid type \"%s\" - types defining "
-						"one data source are supported only (got: %i).",
-						col->type, ds->ds_num);
-				c_psql_shutdown ();
-				return -1;
+			if (rates == NULL) {
+				log_err ("c_psql_write: Failed to determine rate");
+				return NULL;
 			}
 
-			col->ds_type = ds->ds[0].type;
+			status = ssnprintf (str_ptr, str_len,
+					",%lf", rates[i]);
+		}
+		else if (ds->ds[i].type == DS_TYPE_COUNTER)
+			status = ssnprintf (str_ptr, str_len,
+					",%llu", vl->values[i].counter);
+		else if (ds->ds[i].type == DS_TYPE_DERIVE)
+			status = ssnprintf (str_ptr, str_len,
+					",%"PRIi64, vl->values[i].derive);
+		else if (ds->ds[i].type == DS_TYPE_ABSOLUTE)
+			status = ssnprintf (str_ptr, str_len,
+					",%"PRIu64, vl->values[i].absolute);
+
+		if (status < 1) {
+			str_len = 0;
+			break;
+		}
+		else if ((size_t)status >= str_len) {
+			str_len = 0;
+			break;
+		}
+		else {
+			str_ptr += status;
+			str_len -= (size_t)status;
 		}
 	}
 
-	for (i = 0; i < databases_num; ++i) {
-		c_psql_database_t *db = databases + i;
+	sfree (rates);
 
-		char  conninfo[4096];
-		char *buf     = conninfo;
-		int   buf_len = sizeof (conninfo);
-		int   status;
+	if (str_len <= 2) {
+		log_err ("c_psql_write: Failed to stringify value list");
+		return NULL;
+	}
 
-		char *server_host;
-		int   server_version;
+	/* overwrite the first comma */
+	string[0] = '{';
+	str_ptr[0] = '}';
+	str_ptr[1] = '\0';
 
-		int j;
+	return string;
+} /* values_to_sqlarray */
 
-		/* this will happen during reinitialization */
-		if (NULL != db->conn) {
-			c_psql_check_connection (db);
-			continue;
-		}
+static int c_psql_write (const data_set_t *ds, const value_list_t *vl,
+		user_data_t *ud)
+{
+	c_psql_database_t *db;
 
-		status = ssnprintf (buf, buf_len, "dbname = '%s'", db->database);
-		if (0 < status) {
-			buf     += status;
-			buf_len -= status;
-		}
+	char time_str[32];
+	char values_name_str[1024];
+	char values_type_str[1024];
+	char values_str[1024];
 
-		C_PSQL_PAR_APPEND (buf, buf_len, "host",       db->host);
-		C_PSQL_PAR_APPEND (buf, buf_len, "port",       db->port);
-		C_PSQL_PAR_APPEND (buf, buf_len, "user",       db->user);
-		C_PSQL_PAR_APPEND (buf, buf_len, "password",   db->password);
-		C_PSQL_PAR_APPEND (buf, buf_len, "sslmode",    db->sslmode);
-		C_PSQL_PAR_APPEND (buf, buf_len, "krbsrvname", db->krbsrvname);
-		C_PSQL_PAR_APPEND (buf, buf_len, "service",    db->service);
+	const char *params[9];
 
-		db->conn = PQconnectdb (conninfo);
-		if (0 != c_psql_check_connection (db))
-			continue;
+	int success = 0;
+	int i;
 
-		db->proto_version = PQprotocolVersion (db->conn);
+	if ((ud == NULL) || (ud->data == NULL)) {
+		log_err ("c_psql_write: Invalid user data.");
+		return -1;
+	}
 
-		server_host    = PQhost (db->conn);
-		server_version = PQserverVersion (db->conn);
-		log_info ("Sucessfully connected to database %s (user %s) "
-				"at server %s%s%s (server version: %d.%d.%d, "
-				"protocol version: %d, pid: %d)",
-				PQdb (db->conn), PQuser (db->conn),
-				C_PSQL_SOCKET3 (server_host, PQport (db->conn)),
-				C_PSQL_SERVER_VERSION3 (server_version),
-				db->proto_version, PQbackendPID (db->conn));
+	db = ud->data;
+	assert (db->database != NULL);
+	assert (db->writers != NULL);
 
-		if (3 > db->proto_version)
-			log_warn ("Protocol version %d does not support parameters.",
-					db->proto_version);
+	if (cdtime_to_iso8601 (time_str, sizeof (time_str), vl->time) == 0) {
+		log_err ("c_psql_write: Failed to convert time to ISO 8601 format");
+		return -1;
+	}
 
-		/* Now that we know the PostgreSQL server version, we can get the
-		 * right version of each query definition. */
-		for (j = 0; j < db->queries_num; ++j) {
-			c_psql_query_t *tmp;
+	if (values_name_to_sqlarray (ds,
+				values_name_str, sizeof (values_name_str)) == NULL)
+		return -1;
 
-			tmp = c_psql_query_get (db->queries[j]->name, server_version);
+#define VALUE_OR_NULL(v) ((((v) == NULL) || (*(v) == '\0')) ? NULL : (v))
 
-			if (tmp == db->queries[j])
-				continue;
+	params[0] = time_str;
+	params[1] = vl->host;
+	params[2] = vl->plugin;
+	params[3] = VALUE_OR_NULL(vl->plugin_instance);
+	params[4] = vl->type;
+	params[5] = VALUE_OR_NULL(vl->type_instance);
+	params[6] = values_name_str;
 
-			if (NULL == tmp) {
-				log_err ("Query \"%s\" not found for server version %i - "
-						"please check your configuration.",
-						db->queries[j]->name, server_version);
+#undef VALUE_OR_NULL
 
-				if (db->queries_num - j - 1 > 0)
-					memmove (db->queries + j, db->queries + j + 1,
-							(db->queries_num - j - 1) * sizeof (*db->queries));
+	pthread_mutex_lock (&db->db_lock);
 
-				--db->queries_num;
-				--j;
-				continue;
+	if (0 != c_psql_check_connection (db)) {
+		pthread_mutex_unlock (&db->db_lock);
+		return -1;
+	}
+
+	if ((db->commit_interval > 0)
+			&& (db->next_commit == 0))
+		c_psql_begin (db);
+
+	for (i = 0; i < db->writers_num; ++i) {
+		c_psql_writer_t *writer;
+		PGresult *res;
+
+		writer = db->writers[i];
+
+		if (values_type_to_sqlarray (ds,
+					values_type_str, sizeof (values_type_str),
+					writer->store_rates) == NULL) {
+			pthread_mutex_unlock (&db->db_lock);
+			return -1;
+		}
+
+		if (values_to_sqlarray (ds, vl,
+					values_str, sizeof (values_str),
+					writer->store_rates) == NULL) {
+			pthread_mutex_unlock (&db->db_lock);
+			return -1;
+		}
+
+		params[7] = values_type_str;
+		params[8] = values_str;
+
+		res = PQexecParams (db->conn, writer->statement,
+				STATIC_ARRAY_SIZE (params), NULL,
+				(const char *const *)params,
+				NULL, NULL, /* return text data */ 0);
+
+		if ((PGRES_COMMAND_OK != PQresultStatus (res))
+				&& (PGRES_TUPLES_OK != PQresultStatus (res))) {
+			PQclear (res);
+
+			if ((CONNECTION_OK != PQstatus (db->conn))
+					&& (0 == c_psql_check_connection (db))) {
+				/* try again */
+				res = PQexecParams (db->conn, writer->statement,
+						STATIC_ARRAY_SIZE (params), NULL,
+						(const char *const *)params,
+						NULL, NULL, /* return text data */ 0);
+
+				if ((PGRES_COMMAND_OK == PQresultStatus (res))
+						|| (PGRES_TUPLES_OK == PQresultStatus (res))) {
+					PQclear (res);
+					success = 1;
+					continue;
+				}
 			}
 
-			db->queries[j] = tmp;
+			log_err ("Failed to execute SQL query: %s",
+					PQerrorMessage (db->conn));
+			log_info ("SQL query was: '%s', "
+					"params: %s, %s, %s, %s, %s, %s, %s, %s",
+					writer->statement,
+					params[0], params[1], params[2], params[3],
+					params[4], params[5], params[6], params[7]);
+
+			/* this will abort any current transaction -> restart */
+			if (db->next_commit > 0)
+				c_psql_commit (db);
+
+			pthread_mutex_unlock (&db->db_lock);
+			return -1;
 		}
+
+		PQclear (res);
+		success = 1;
 	}
 
-	plugin_register_read ("postgresql", c_psql_read);
-	plugin_register_shutdown ("postgresql", c_psql_shutdown);
-	return 0;
-} /* c_psql_init */
+	if ((db->next_commit > 0)
+			&& (cdtime () > db->next_commit))
+		c_psql_commit (db);
+
+	pthread_mutex_unlock (&db->db_lock);
 
-static int config_set_s (char *name, char **var, const oconfig_item_t *ci)
+	if (! success)
+		return -1;
+	return 0;
+} /* c_psql_write */
+
+/* We cannot flush single identifiers as all we do is to commit the currently
+ * running transaction, thus making sure that all written data is actually
+ * visible to everybody. */
+static int c_psql_flush (cdtime_t timeout,
+		__attribute__((unused)) const char *ident,
+		user_data_t *ud)
 {
-	if ((0 != ci->children_num) || (1 != ci->values_num)
-			|| (OCONFIG_TYPE_STRING != ci->values[0].type)) {
-		log_err ("%s expects a single string argument.", name);
-		return 1;
+	c_psql_database_t **dbs = databases;
+	size_t dbs_num = databases_num;
+	size_t i;
+
+	if ((ud != NULL) && (ud->data != NULL)) {
+		dbs = (void *)&ud->data;
+		dbs_num = 1;
 	}
 
-	sfree (*var);
-	*var = sstrdup (ci->values[0].value.string);
+	for (i = 0; i < dbs_num; ++i) {
+		c_psql_database_t *db = dbs[i];
+
+		/* don't commit if the timeout is larger than the regular commit
+		 * interval as in that case all requested data has already been
+		 * committed */
+		if ((db->next_commit > 0) && (db->commit_interval > timeout))
+			c_psql_commit (db);
+	}
 	return 0;
-} /* config_set_s */
+} /* c_psql_flush */
 
-static int config_set_i (char *name, int *var, const oconfig_item_t *ci)
+static int c_psql_shutdown (void)
 {
-	if ((0 != ci->children_num) || (1 != ci->values_num)
-			|| (OCONFIG_TYPE_NUMBER != ci->values[0].type)) {
-		log_err ("%s expects a single number argument.", name);
-		return 1;
+	size_t i = 0;
+
+	_Bool had_flush = 0;
+
+	plugin_unregister_read_group ("postgresql");
+
+	for (i = 0; i < databases_num; ++i) {
+		c_psql_database_t *db = databases[i];
+
+		if (db->writers_num > 0) {
+			char cb_name[DATA_MAX_NAME_LEN];
+			ssnprintf (cb_name, sizeof (cb_name), "postgresql-%s",
+					db->database);
+
+			if (! had_flush) {
+				plugin_unregister_flush ("postgresql");
+				had_flush = 1;
+			}
+
+			plugin_unregister_flush (cb_name);
+			plugin_unregister_write (cb_name);
+		}
+
+		sfree (db);
 	}
 
-	*var = (int)ci->values[0].value.number;
+	udb_query_free (queries, queries_num);
+	queries = NULL;
+	queries_num = 0;
+
+	sfree (writers);
+	writers = NULL;
+	writers_num = 0;
+
+	sfree (databases);
+	databases = NULL;
+	databases_num = 0;
+
 	return 0;
-} /* config_set_i */
+} /* c_psql_shutdown */
 
-static int config_set_param (c_psql_query_t *query, const oconfig_item_t *ci)
+static int config_query_param_add (udb_query_t *q, oconfig_item_t *ci)
 {
-	c_psql_param_t param;
-	char          *param_str;
+	c_psql_user_data_t *data;
+	const char *param_str;
 
-	if ((0 != ci->children_num) || (1 != ci->values_num)
-			|| (OCONFIG_TYPE_STRING != ci->values[0].type)) {
-		log_err ("Param expects a single string argument.");
-		return 1;
+	c_psql_param_t *tmp;
+
+	data = udb_query_get_user_data (q);
+	if (NULL == data) {
+		data = (c_psql_user_data_t *) smalloc (sizeof (*data));
+		if (NULL == data) {
+			log_err ("Out of memory.");
+			return -1;
+		}
+		memset (data, 0, sizeof (*data));
+		data->params = NULL;
 	}
 
+	tmp = (c_psql_param_t *) realloc (data->params,
+			(data->params_num + 1) * sizeof (c_psql_param_t));
+	if (NULL == tmp) {
+		log_err ("Out of memory.");
+		return -1;
+	}
+	data->params = tmp;
+
 	param_str = ci->values[0].value.string;
 	if (0 == strcasecmp (param_str, "hostname"))
-		param = C_PSQL_PARAM_HOST;
+		data->params[data->params_num] = C_PSQL_PARAM_HOST;
 	else if (0 == strcasecmp (param_str, "database"))
-		param = C_PSQL_PARAM_DB;
+		data->params[data->params_num] = C_PSQL_PARAM_DB;
 	else if (0 == strcasecmp (param_str, "username"))
-		param = C_PSQL_PARAM_USER;
+		data->params[data->params_num] = C_PSQL_PARAM_USER;
+	else if (0 == strcasecmp (param_str, "interval"))
+		data->params[data->params_num] = C_PSQL_PARAM_INTERVAL;
+	else if (0 == strcasecmp (param_str, "instance"))
+		data->params[data->params_num] = C_PSQL_PARAM_INSTANCE;
 	else {
 		log_err ("Invalid parameter \"%s\".", param_str);
 		return 1;
 	}
 
-	++query->params_num;
-	if (NULL == (query->params = (c_psql_param_t *)realloc (query->params,
-				query->params_num * sizeof (*query->params)))) {
-		log_err ("Out of memory.");
-		exit (5);
-	}
+	data->params_num++;
+	udb_query_set_user_data (q, data);
 
-	query->params[query->params_num - 1] = param;
-	return 0;
-} /* config_set_param */
+	return (0);
+} /* config_query_param_add */
 
-static int config_set_column (c_psql_query_t *query, const oconfig_item_t *ci)
+static int config_query_callback (udb_query_t *q, oconfig_item_t *ci)
 {
-	c_psql_col_t *col;
+	if (0 == strcasecmp ("Param", ci->key))
+		return config_query_param_add (q, ci);
 
-	int i;
+	log_err ("Option not allowed within a Query block: `%s'", ci->key);
 
-	if ((0 != ci->children_num)
-			|| (1 > ci->values_num) || (2 < ci->values_num)) {
-		log_err ("Column expects either one or two arguments.");
-		return 1;
-	}
+	return (-1);
+} /* config_query_callback */
 
-	for (i = 0; i < ci->values_num; ++i) {
-		if (OCONFIG_TYPE_STRING != ci->values[i].type) {
-			log_err ("Column expects either one or two string arguments.");
-			return 1;
-		}
-	}
+static int config_add_writer (oconfig_item_t *ci,
+		c_psql_writer_t *src_writers, size_t src_writers_num,
+		c_psql_writer_t ***dst_writers, size_t *dst_writers_num)
+{
+	char *name;
 
-	++query->cols_num;
-	if (NULL == (query->cols = (c_psql_col_t *)realloc (query->cols,
-				query->cols_num * sizeof (*query->cols)))) {
-		log_err ("Out of memory.");
-		exit (5);
+	size_t i;
+
+	if ((ci == NULL) || (dst_writers == NULL) || (dst_writers_num == NULL))
+		return -1;
+
+	if ((ci->values_num != 1)
+			|| (ci->values[0].type != OCONFIG_TYPE_STRING)) {
+		log_err ("`Writer' expects a single string argument.");
+		return 1;
 	}
 
-	col = query->cols + query->cols_num - 1;
+	name = ci->values[0].value.string;
 
-	col->ds_type = -1;
+	for (i = 0; i < src_writers_num; ++i) {
+		c_psql_writer_t **tmp;
 
-	col->type = sstrdup (ci->values[0].value.string);
-	col->type_instance = (2 == ci->values_num)
-		? sstrdup (ci->values[1].value.string) : NULL;
-	return 0;
-} /* config_set_column */
+		if (strcasecmp (name, src_writers[i].name) != 0)
+			continue;
 
-static int set_query (c_psql_database_t *db, const char *name)
-{
-	c_psql_query_t *query;
+		tmp = (c_psql_writer_t **)realloc (*dst_writers,
+				sizeof (**dst_writers) * (*dst_writers_num + 1));
+		if (tmp == NULL) {
+			log_err ("Out of memory.");
+			return -1;
+		}
 
-	query = c_psql_query_get (name, -1);
-	if (NULL == query) {
-		log_err ("Query \"%s\" not found - please check your configuration.",
-				name);
-		return 1;
-	}
+		tmp[*dst_writers_num] = src_writers + i;
 
-	++db->queries_num;
-	if (NULL == (db->queries = (c_psql_query_t **)realloc (db->queries,
-				db->queries_num * sizeof (*db->queries)))) {
-		log_err ("Out of memory.");
-		exit (5);
+		*dst_writers = tmp;
+		++(*dst_writers_num);
+		break;
 	}
 
-	if (query->params_num > db->max_params_num)
-		db->max_params_num = query->params_num;
+	if (i >= src_writers_num) {
+		log_err ("No such writer: `%s'", name);
+		return -1;
+	}
 
-	db->queries[db->queries_num - 1] = query;
 	return 0;
-} /* set_query */
-
-static int config_set_query (c_psql_database_t *db, const oconfig_item_t *ci)
-{
-	if ((0 != ci->children_num) || (1 != ci->values_num)
-			|| (OCONFIG_TYPE_STRING != ci->values[0].type)) {
-		log_err ("Query expects a single string argument.");
-		return 1;
-	}
-	return set_query (db, ci->values[0].value.string);
-} /* config_set_query */
+} /* config_add_writer */
 
-static int c_psql_config_query (oconfig_item_t *ci)
+static int c_psql_config_writer (oconfig_item_t *ci)
 {
-	c_psql_query_t *query;
+	c_psql_writer_t *writer;
+	c_psql_writer_t *tmp;
 
+	int status = 0;
 	int i;
 
-	if ((1 != ci->values_num)
-			|| (OCONFIG_TYPE_STRING != ci->values[0].type)) {
-		log_err ("<Query> expects a single string argument.");
+	if ((ci->values_num != 1)
+			|| (ci->values[0].type != OCONFIG_TYPE_STRING)) {
+		log_err ("<Writer> expects a single string argument.");
 		return 1;
 	}
 
-	query = c_psql_query_new (ci->values[0].value.string);
+	tmp = (c_psql_writer_t *)realloc (writers,
+			sizeof (*writers) * (writers_num + 1));
+	if (tmp == NULL) {
+		log_err ("Out of memory.");
+		return -1;
+	}
+
+	writers = tmp;
+	writer  = writers + writers_num;
+	++writers_num;
+
+	writer->name = sstrdup (ci->values[0].value.string);
+	writer->statement = NULL;
+	writer->store_rates = 1;
 
 	for (i = 0; i < ci->children_num; ++i) {
 		oconfig_item_t *c = ci->children + i;
 
-		if (0 == strcasecmp (c->key, "Query"))
-			config_set_s ("Query", &query->query, c);
-		else if (0 == strcasecmp (c->key, "Param"))
-			config_set_param (query, c);
-		else if (0 == strcasecmp (c->key, "Column"))
-			config_set_column (query, c);
-		else if (0 == strcasecmp (c->key, "MinPGVersion"))
-			config_set_i ("MinPGVersion", &query->min_pg_version, c);
-		else if (0 == strcasecmp (c->key, "MaxPGVersion"))
-			config_set_i ("MaxPGVersion", &query->max_pg_version, c);
+		if (strcasecmp ("Statement", c->key) == 0)
+			status = cf_util_get_string (c, &writer->statement);
+		else if (strcasecmp ("StoreRates", c->key) == 0)
+			status = cf_util_get_boolean (c, &writer->store_rates);
 		else
 			log_warn ("Ignoring unknown config key \"%s\".", c->key);
 	}
 
-	for (i = 0; i < queries_num - 1; ++i) {
-		c_psql_query_t *q = queries + i;
-
-		if ((0 == strcasecmp (q->name, query->name))
-				&& (q->min_pg_version <= query->max_pg_version)
-				&& (query->min_pg_version <= q->max_pg_version)) {
-			log_err ("Ignoring redefinition (with overlapping version ranges) "
-					"of query \"%s\".", query->name);
-			c_psql_query_delete (query);
-			--queries_num;
-			return 1;
-		}
+	if (status != 0) {
+		sfree (writer->statement);
+		sfree (writer->name);
+		sfree (writer);
+		return status;
 	}
 
-	if (query->min_pg_version > query->max_pg_version) {
-		log_err ("Query \"%s\": MinPGVersion > MaxPGVersion.",
-				query->name);
-		c_psql_query_delete (query);
-		--queries_num;
-		return 1;
-	}
-
-	if (NULL == query->query) {
-		log_err ("Query \"%s\" does not include an SQL query string - "
-				"please check your configuration.", query->name);
-		c_psql_query_delete (query);
-		--queries_num;
-		return 1;
-	}
 	return 0;
-} /* c_psql_config_query */
+} /* c_psql_config_writer */
 
 static int c_psql_config_database (oconfig_item_t *ci)
 {
 	c_psql_database_t *db;
 
+	char cb_name[DATA_MAX_NAME_LEN];
+	struct timespec cb_interval = { 0, 0 };
+	user_data_t ud;
+
+	static _Bool have_flush = 0;
+
 	int i;
 
 	if ((1 != ci->values_num)
@@ -829,37 +1206,115 @@ static int c_psql_config_database (oconfig_item_t *ci)
 		return 1;
 	}
 
+	memset (&ud, 0, sizeof (ud));
+
 	db = c_psql_database_new (ci->values[0].value.string);
+	if (db == NULL)
+		return -1;
 
 	for (i = 0; i < ci->children_num; ++i) {
 		oconfig_item_t *c = ci->children + i;
 
 		if (0 == strcasecmp (c->key, "Host"))
-			config_set_s ("Host", &db->host, c);
+			cf_util_get_string (c, &db->host);
 		else if (0 == strcasecmp (c->key, "Port"))
-			config_set_s ("Port", &db->port, c);
+			cf_util_get_service (c, &db->port);
 		else if (0 == strcasecmp (c->key, "User"))
-			config_set_s ("User", &db->user, c);
+			cf_util_get_string (c, &db->user);
 		else if (0 == strcasecmp (c->key, "Password"))
-			config_set_s ("Password", &db->password, c);
+			cf_util_get_string (c, &db->password);
+		else if (0 == strcasecmp (c->key, "Instance"))
+			cf_util_get_string (c, &db->instance);
 		else if (0 == strcasecmp (c->key, "SSLMode"))
-			config_set_s ("SSLMode", &db->sslmode, c);
+			cf_util_get_string (c, &db->sslmode);
 		else if (0 == strcasecmp (c->key, "KRBSrvName"))
-			config_set_s ("KRBSrvName", &db->krbsrvname, c);
+			cf_util_get_string (c, &db->krbsrvname);
 		else if (0 == strcasecmp (c->key, "Service"))
-			config_set_s ("Service", &db->service, c);
+			cf_util_get_string (c, &db->service);
 		else if (0 == strcasecmp (c->key, "Query"))
-			config_set_query (db, c);
+			udb_query_pick_from_list (c, queries, queries_num,
+					&db->queries, &db->queries_num);
+		else if (0 == strcasecmp (c->key, "Writer"))
+			config_add_writer (c, writers, writers_num,
+					&db->writers, &db->writers_num);
+		else if (0 == strcasecmp (c->key, "Interval"))
+			cf_util_get_cdtime (c, &db->interval);
+		else if (strcasecmp ("CommitInterval", c->key) == 0)
+			cf_util_get_cdtime (c, &db->commit_interval);
 		else
 			log_warn ("Ignoring unknown config key \"%s\".", c->key);
 	}
 
-	if (NULL == db->queries) {
-		for (i = 0; i < def_queries_num; ++i)
-			set_query (db, def_queries[i]);
+	/* If no `Query' options were given, add the default queries.. */
+	if ((db->queries_num == 0) && (db->writers_num == 0)){
+		for (i = 0; i < def_queries_num; i++)
+			udb_query_pick_from_list_by_name (def_queries[i],
+					queries, queries_num,
+					&db->queries, &db->queries_num);
+	}
+
+	if (db->queries_num > 0) {
+		db->q_prep_areas = (udb_query_preparation_area_t **) calloc (
+				db->queries_num, sizeof (*db->q_prep_areas));
+
+		if (db->q_prep_areas == NULL) {
+			log_err ("Out of memory.");
+			c_psql_database_delete (db);
+			return -1;
+		}
+	}
+
+	for (i = 0; (size_t)i < db->queries_num; ++i) {
+		c_psql_user_data_t *data;
+		data = udb_query_get_user_data (db->queries[i]);
+		if ((data != NULL) && (data->params_num > db->max_params_num))
+			db->max_params_num = data->params_num;
+
+		db->q_prep_areas[i]
+			= udb_query_allocate_preparation_area (db->queries[i]);
+
+		if (db->q_prep_areas[i] == NULL) {
+			log_err ("Out of memory.");
+			c_psql_database_delete (db);
+			return -1;
+		}
+	}
+
+	ud.data = db;
+	ud.free_func = c_psql_database_delete;
+
+	ssnprintf (cb_name, sizeof (cb_name), "postgresql-%s", db->instance);
+
+	if (db->queries_num > 0) {
+		CDTIME_T_TO_TIMESPEC (db->interval, &cb_interval);
+
+		++db->ref_cnt;
+		plugin_register_complex_read ("postgresql", cb_name, c_psql_read,
+				/* interval = */ (db->interval > 0) ? &cb_interval : NULL,
+				&ud);
+	}
+	if (db->writers_num > 0) {
+		++db->ref_cnt;
+		plugin_register_write (cb_name, c_psql_write, &ud);
+
+		if (! have_flush) {
+			/* flush all */
+			plugin_register_flush ("postgresql",
+					c_psql_flush, /* user data = */ NULL);
+			have_flush = 1;
+		}
+
+		/* flush this connection only */
+		++db->ref_cnt;
+		plugin_register_flush (cb_name, c_psql_flush, &ud);
+	}
+	else if (db->commit_interval > 0) {
+		log_warn ("Database '%s': You do not have any writers assigned to "
+				"this database connection. Setting 'CommitInterval' does "
+				"not have any effect.", db->database);
 	}
 	return 0;
-}
+} /* c_psql_config_database */
 
 static int c_psql_config (oconfig_item_t *ci)
 {
@@ -887,7 +1342,10 @@ static int c_psql_config (oconfig_item_t *ci)
 		oconfig_item_t *c = ci->children + i;
 
 		if (0 == strcasecmp (c->key, "Query"))
-			c_psql_config_query (c);
+			udb_query_create (&queries, &queries_num, c,
+					/* callback = */ config_query_callback);
+		else if (0 == strcasecmp (c->key, "Writer"))
+			c_psql_config_writer (c);
 		else if (0 == strcasecmp (c->key, "Database"))
 			c_psql_config_database (c);
 		else
@@ -899,8 +1357,7 @@ static int c_psql_config (oconfig_item_t *ci)
 void module_register (void)
 {
 	plugin_register_complex_config ("postgresql", c_psql_config);
-	plugin_register_init ("postgresql", c_psql_init);
+	plugin_register_shutdown ("postgresql", c_psql_shutdown);
 } /* module_register */
 
 /* vim: set sw=4 ts=4 tw=78 noexpandtab : */
-