X-Git-Url: https://git.octo.it/?p=collectd.git;a=blobdiff_plain;f=src%2Fpostgresql.c;h=635abfca61bf5647b4d53cea55601a5182a8997e;hp=a8812e2158327bf86153689894e8eada7e620022;hb=633c3966f770e4d46651a2fe219a18d8a9907a9f;hpb=59c7ee1cafaf53814838794908dd84f8101334c7

diff --git a/src/postgresql.c b/src/postgresql.c
index a8812e21..635abfca 100644
--- a/src/postgresql.c
+++ b/src/postgresql.c
@@ -1,35 +1,29 @@
 /**
  * collectd - src/postgresql.c
- * Copyright (C) 2008, 2009  Sebastian Harl
- * Copyright (C) 2009        Florian Forster
- * All rights reserved.
+ * Copyright (C) 2008-2012  Sebastian Harl
+ * Copyright (C) 2009       Florian Forster
  *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
  *
- * - Redistributions of source code must retain the above copyright
- *   notice, this list of conditions and the following disclaimer.
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
  *
- * - 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.
- *
- * 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.
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
  *
  * Authors:
  *   Sebastian Harl <sh at tokkee.org>
- *   Florian Forster <octo at verplant.org>
+ *   Florian Forster <octo at collectd.org>
  **/
 
 /*
@@ -42,15 +36,21 @@
 #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"
@@ -95,6 +95,7 @@ typedef enum {
 	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. */
@@ -104,6 +105,12 @@ typedef struct {
 } c_psql_user_data_t;
 
 typedef struct {
+	char *name;
+	char *statement;
+	_Bool store_rates;
+} c_psql_writer_t;
+
+typedef struct {
 	PGconn      *conn;
 	c_complain_t conn_complaint;
 
@@ -117,19 +124,33 @@ typedef struct {
 	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;
 	char *database;
 	char *user;
 	char *password;
 
+	char *instance;
+
 	char *sslmode;
 
 	char *krbsrvname;
 
 	char *service;
+
+	int ref_cnt;
 } c_psql_database_t;
 
 static char *def_queries[] = {
@@ -143,19 +164,77 @@ static char *def_queries[] = {
 };
 static int def_queries_num = STATIC_ARRAY_SIZE (def_queries);
 
-static udb_query_t      **queries       = NULL;
-static size_t             queries_num   = 0;
+static c_psql_database_t **databases     = NULL;
+static size_t              databases_num = 0;
+
+static udb_query_t       **queries       = NULL;
+static size_t              queries_num   = 0;
+
+static c_psql_writer_t    *writers       = NULL;
+static size_t              writers_num   = 0;
+
+static int c_psql_begin (c_psql_database_t *db)
+{
+	PGresult *r = PQexec (db->conn, "BEGIN");
+
+	int status = 1;
+
+	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);
+	}
+	return status;
+} /* c_psql_begin */
+
+static int c_psql_commit (c_psql_database_t *db)
+{
+	PGresult *r = PQexec (db->conn, "COMMIT");
+
+	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;
 
-	db = (c_psql_database_t *)malloc (sizeof (*db));
+	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.");
+		sfree (db);
+		return NULL;
+	}
+
+	databases = tmp;
+	databases[databases_num] = db;
+	++databases_num;
+
 	db->conn = NULL;
 
 	C_COMPLAIN_INIT (&db->conn_complaint);
@@ -169,19 +248,31 @@ static c_psql_database_t *c_psql_database_new (const char *name)
 	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;
 	db->port       = NULL;
 	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 */
 
@@ -191,6 +282,17 @@ static void c_psql_database_delete (void *data)
 
 	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;
 
@@ -202,17 +304,31 @@ static void c_psql_database_delete (void *data)
 	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 */
 
@@ -223,7 +339,7 @@ static int c_psql_connect (c_psql_database_t *db)
 	int   buf_len = sizeof (conninfo);
 	int   status;
 
-	if (! db)
+	if ((! db) || (! db->database))
 		return -1;
 
 	status = ssnprintf (buf, buf_len, "dbname = '%s'", db->database);
@@ -259,9 +375,6 @@ static int c_psql_check_connection (c_psql_database_t *db)
 		c_psql_connect (db);
 	}
 
-	/* "ping" */
-	PQclear (PQexec (db->conn, "SELECT 42;"));
-
 	if (CONNECTION_OK != PQstatus (db->conn)) {
 		PQreset (db->conn);
 
@@ -271,8 +384,9 @@ 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;
 		}
 
@@ -337,9 +451,13 @@ static PGresult *c_psql_exec_query_params (c_psql_database_t *db,
 			case C_PSQL_PARAM_INTERVAL:
 				ssnprintf (interval, sizeof (interval), "%.3f",
 						(db->interval > 0)
-						? CDTIME_T_TO_DOUBLE (db->interval) : interval_g);
+						? 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);
 		}
@@ -351,6 +469,7 @@ static PGresult *c_psql_exec_query_params (c_psql_database_t *db,
 			NULL, NULL, /* return text data */ 0);
 } /* c_psql_exec_query_params */
 
+/* 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)
 {
@@ -377,30 +496,46 @@ static int c_psql_exec_query (c_psql_database_t *db, udb_query_t *q,
 	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,
+		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;
 
-#define BAIL_OUT(status) \
-	sfree (column_names); \
-	sfree (column_values); \
-	PQclear (res); \
-	return status
-
 	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",
 				udb_query_get_statement (q));
-		BAIL_OUT (-1);
+		PQclear (res);
+		return -1;
 	}
 
+#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);
@@ -430,13 +565,14 @@ static int c_psql_exec_query (c_psql_database_t *db, udb_query_t *q,
 	}
 
 	if (C_PSQL_IS_UNIX_DOMAIN_SOCKET (db->host)
+			|| (0 == strcmp (db->host, "127.0.0.1"))
 			|| (0 == strcmp (db->host, "localhost")))
 		host = hostname_g;
 	else
 		host = db->host;
 
 	status = udb_query_prepare_result (q, prep_area, host, "postgresql",
-			db->database, column_names, (size_t) column_num, db->interval);
+			db->instance, column_names, (size_t) column_num, db->interval);
 	if (0 != status) {
 		log_err ("udb_query_prepare_result failed with status %i.",
 				status);
@@ -487,9 +623,15 @@ static int c_psql_read (user_data_t *ud)
 	db = ud->data;
 
 	assert (NULL != db->database);
+	assert (NULL != db->instance);
+	assert (NULL != db->queries);
+
+	pthread_mutex_lock (&db->db_lock);
 
-	if (0 != c_psql_check_connection (db))
+	if (0 != c_psql_check_connection (db)) {
+		pthread_mutex_unlock (&db->db_lock);
 		return -1;
+	}
 
 	for (i = 0; i < db->queries_num; ++i)
 	{
@@ -507,34 +649,384 @@ static int c_psql_read (user_data_t *ud)
 			success = 1;
 	}
 
+	pthread_mutex_unlock (&db->db_lock);
+
 	if (! success)
 		return -1;
 	return 0;
 } /* c_psql_read */
 
+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;
+
+	str_ptr = string;
+	str_len = string_len;
+
+	for (i = 0; i < ds->ds_num; ++i) {
+		int status = ssnprintf (str_ptr, str_len, ",'%s'", ds->ds[i].name);
+
+		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;
+		}
+	}
+
+	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 */
+
+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;
+		}
+	}
+
+	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';
+
+	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;
+
+	str_ptr = string;
+	str_len = string_len;
+
+	for (i = 0; i < vl->values_len; ++i) {
+		int status = 0;
+
+		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;
+		}
+
+		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 (rates == NULL) {
+				log_err ("c_psql_write: Failed to determine rate");
+				return NULL;
+			}
+
+			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;
+		}
+	}
+
+	sfree (rates);
+
+	if (str_len <= 2) {
+		log_err ("c_psql_write: Failed to stringify value list");
+		return NULL;
+	}
+
+	/* overwrite the first comma */
+	string[0] = '{';
+	str_ptr[0] = '}';
+	str_ptr[1] = '\0';
+
+	return string;
+} /* values_to_sqlarray */
+
+static int c_psql_write (const data_set_t *ds, const value_list_t *vl,
+		user_data_t *ud)
+{
+	c_psql_database_t *db;
+
+	char time_str[32];
+	char values_name_str[1024];
+	char values_type_str[1024];
+	char values_str[1024];
+
+	const char *params[9];
+
+	int success = 0;
+	int i;
+
+	if ((ud == NULL) || (ud->data == NULL)) {
+		log_err ("c_psql_write: Invalid user data.");
+		return -1;
+	}
+
+	db = ud->data;
+	assert (db->database != NULL);
+	assert (db->writers != NULL);
+
+	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;
+	}
+
+	if (values_name_to_sqlarray (ds,
+				values_name_str, sizeof (values_name_str)) == NULL)
+		return -1;
+
+#define VALUE_OR_NULL(v) ((((v) == NULL) || (*(v) == '\0')) ? NULL : (v))
+
+	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;
+
+#undef VALUE_OR_NULL
+
+	pthread_mutex_lock (&db->db_lock);
+
+	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;
+				}
+			}
+
+			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;
+	}
+
+	if ((db->next_commit > 0)
+			&& (cdtime () > db->next_commit))
+		c_psql_commit (db);
+
+	pthread_mutex_unlock (&db->db_lock);
+
+	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)
+{
+	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;
+	}
+
+	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;
+} /* c_psql_flush */
+
 static int c_psql_shutdown (void)
 {
+	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);
+	}
+
 	udb_query_free (queries, queries_num);
 	queries = NULL;
 	queries_num = 0;
 
-	return 0;
-} /* c_psql_shutdown */
+	sfree (writers);
+	writers = NULL;
+	writers_num = 0;
 
-static int config_set_s (char *name, char **var, const oconfig_item_t *ci)
-{
-	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;
-	}
+	sfree (databases);
+	databases = NULL;
+	databases_num = 0;
 
-	sfree (*var);
-	*var = sstrdup (ci->values[0].value.string);
 	return 0;
-} /* config_set_s */
+} /* c_psql_shutdown */
 
 static int config_query_param_add (udb_query_t *q, oconfig_item_t *ci)
 {
@@ -571,6 +1063,8 @@ static int config_query_param_add (udb_query_t *q, oconfig_item_t *ci)
 		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;
@@ -592,6 +1086,103 @@ static int config_query_callback (udb_query_t *q, oconfig_item_t *ci)
 	return (-1);
 } /* config_query_callback */
 
+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;
+
+	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;
+	}
+
+	name = ci->values[0].value.string;
+
+	for (i = 0; i < src_writers_num; ++i) {
+		c_psql_writer_t **tmp;
+
+		if (strcasecmp (name, src_writers[i].name) != 0)
+			continue;
+
+		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;
+		}
+
+		tmp[*dst_writers_num] = src_writers + i;
+
+		*dst_writers = tmp;
+		++(*dst_writers_num);
+		break;
+	}
+
+	if (i >= src_writers_num) {
+		log_err ("No such writer: `%s'", name);
+		return -1;
+	}
+
+	return 0;
+} /* config_add_writer */
+
+static int c_psql_config_writer (oconfig_item_t *ci)
+{
+	c_psql_writer_t *writer;
+	c_psql_writer_t *tmp;
+
+	int status = 0;
+	int i;
+
+	if ((ci->values_num != 1)
+			|| (ci->values[0].type != OCONFIG_TYPE_STRING)) {
+		log_err ("<Writer> expects a single string argument.");
+		return 1;
+	}
+
+	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 (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);
+	}
+
+	if (status != 0) {
+		sfree (writer->statement);
+		sfree (writer->name);
+		sfree (writer);
+		return status;
+	}
+
+	return 0;
+} /* c_psql_config_writer */
+
 static int c_psql_config_database (oconfig_item_t *ci)
 {
 	c_psql_database_t *db;
@@ -600,6 +1191,8 @@ static int c_psql_config_database (oconfig_item_t *ci)
 	struct timespec cb_interval = { 0, 0 };
 	user_data_t ud;
 
+	static _Bool have_flush = 0;
+
 	int i;
 
 	if ((1 != ci->values_num)
@@ -618,30 +1211,37 @@ static int c_psql_config_database (oconfig_item_t *ci)
 		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"))
 			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 no `Query' options were given, add the default queries.. */
-	if (db->queries_num == 0) {
+	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,
@@ -678,13 +1278,36 @@ static int c_psql_config_database (oconfig_item_t *ci)
 	ud.data = db;
 	ud.free_func = c_psql_database_delete;
 
-	ssnprintf (cb_name, sizeof (cb_name), "postgresql-%s", db->database);
+	ssnprintf (cb_name, sizeof (cb_name), "postgresql-%s", db->instance);
+
+	if (db->queries_num > 0) {
+		CDTIME_T_TO_TIMESPEC (db->interval, &cb_interval);
 
-	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;
+		}
 
-	plugin_register_complex_read ("postgresql", cb_name, c_psql_read,
-			/* interval = */ (db->interval > 0) ? &cb_interval : NULL,
-			&ud);
+		/* 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 */
 
@@ -716,6 +1339,8 @@ static int c_psql_config (oconfig_item_t *ci)
 		if (0 == strcasecmp (c->key, "Query"))
 			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