contrib/postgresql/collectd_insert.sql: Added sample writer setup.

diff --git a/contrib/postgresql/collectd_insert.sql b/contrib/postgresql/collectd_insert.sql
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+-- collectd - contrib/postgresql/collectd_insert.sql
+-- Copyright (C) 2012 Sebastian 'tokkee' Harl
+-- All rights reserved.
+--
+-- Redistribution and use in source and binary forms, with or without
+-- modification, are permitted provided that the following conditions
+-- are met:
+--
+-- - Redistributions of source code must retain the above copyright
+--   notice, this list of conditions and the following disclaimer.
+--
+-- - 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.
+
+-- Description:
+-- ------------
+--
+-- This is a sample database setup that may be used to write data collected by
+-- collectd to a PostgreSQL database. We're using two tables, 'identifiers'
+-- and 'values' to store the value-list identifier and the actual values
+-- respectively.
+--
+-- The 'values' table is partitioned to improve performance and maintainance.
+-- Please note that additional maintainance scripts are required in order to
+-- keep the setup running -- see the comments below for details.
+--
+-- The function 'collectd_insert' may be used to actually insert values
+-- submitted by collectd into those tables.
+--
+-- Sample configuration:
+-- ---------------------
+--
+-- <Plugin postgresql>
+--     <Writer sqlstore>
+--         Statement "SELECT collectd_insert($1, $2, $3, $4, $5, $6, $7, $8, $9);"
+--     </Writer>
+--     <Database foo>
+--         # ...
+--         Writer sqlstore
+--     </Database>
+-- </Plugin>
+
+CREATE TABLE identifiers (
+    id integer NOT NULL,
+    host character varying(64) NOT NULL,
+    plugin character varying(64) NOT NULL,
+    plugin_inst character varying(64) DEFAULT NULL::character varying,
+    type character varying(64) NOT NULL,
+    type_inst character varying(64) DEFAULT NULL::character varying
+);
+CREATE SEQUENCE identifiers_id_seq
+    START WITH 1
+    INCREMENT BY 1
+    NO MINVALUE
+    NO MAXVALUE
+    CACHE 1;
+ALTER SEQUENCE identifiers_id_seq OWNED BY identifiers.id;
+ALTER TABLE ONLY identifiers
+    ALTER COLUMN id SET DEFAULT nextval('identifiers_id_seq'::regclass);
+ALTER TABLE ONLY identifiers
+    ADD CONSTRAINT identifiers_host_plugin_plugin_inst_type_type_inst_key
+        UNIQUE (host, plugin, plugin_inst, type, type_inst);
+ALTER TABLE ONLY identifiers
+    ADD CONSTRAINT identifiers_pkey PRIMARY KEY (id);
+
+-- optionally, create indexes for the identifier fields
+CREATE INDEX identifiers_host ON identifiers USING btree (host);
+CREATE INDEX identifiers_plugin ON identifiers USING btree (plugin);
+CREATE INDEX identifiers_plugin_inst ON identifiers USING btree (plugin_inst);
+CREATE INDEX identifiers_type ON identifiers USING btree (type);
+CREATE INDEX identifiers_type_inst ON identifiers USING btree (type_inst);
+
+CREATE TABLE "values" (
+    id integer NOT NULL,
+    tstamp timestamp without time zone NOT NULL,
+    name character varying(64) NOT NULL,
+    value double precision NOT NULL
+);
+
+-- partition "values" by day (or week, month, ...)
+-- make sure the CHECKs don't overlap!
+CREATE TABLE "values$2012-08-19" (
+    CHECK (tstamp >= TIMESTAMP '2012-08-19' AND tstamp < TIMESTAMP '2012-08-20')
+) INHERITS (values);
+CREATE TABLE "values$2012-08-20" (
+    CHECK (tstamp >= TIMESTAMP '2012-08-20' AND tstamp < TIMESTAMP '2012-08-21')
+) INHERITS (values);
+-- ...
+-- set up a daily (weekly, monthly, ...) cron-job (or similar) to create the
+-- tables for the next day (week, month, ...)
+
+ALTER TABLE ONLY "values$2012-08-19"
+    ADD CONSTRAINT "values_2012-08-19_pkey" PRIMARY KEY (id, tstamp, name, value);
+ALTER TABLE ONLY "values$2012-08-19"
+    ADD CONSTRAINT "values_2012-08-19_id_fkey" FOREIGN KEY (id) REFERENCES identifiers(id);
+
+ALTER TABLE ONLY "values$2012-08-20"
+    ADD CONSTRAINT "values_2012-08-20_pkey" PRIMARY KEY (id, tstamp, name, value);
+ALTER TABLE ONLY "values$2012-08-20"
+    ADD CONSTRAINT "values_2012-08-20_id_fkey" FOREIGN KEY (id) REFERENCES identifiers(id);
+-- ...
+
+CREATE OR REPLACE FUNCTION values_insert_trigger()
+    RETURNS trigger
+    LANGUAGE plpgsql
+    AS $_$
+DECLARE
+    child_tbl character varying;
+BEGIN
+    SELECT 'values$' || CAST (NEW.tstamp AS DATE) INTO child_tbl;
+    -- Rather than using 'EXECUTE', some if-cascade checking the date may also
+    -- be used. However, this would require frequent updates of the trigger
+    -- function while this example works automatically.
+    EXECUTE 'INSERT INTO "' || child_tbl || '" VALUES ($1.*)' USING NEW;
+    RETURN NULL;
+END;
+$_$;
+
+CREATE TRIGGER insert_values_trigger
+    BEFORE INSERT ON values
+    FOR EACH ROW EXECUTE PROCEDURE values_insert_trigger();
+
+-- when querying values make sure to enable constraint exclusion
+-- SET constraint_exclusion = on;
+
+CREATE OR REPLACE FUNCTION collectd_insert(
+        timestamp, character varying,
+        character varying, character varying,
+        character varying, character varying,
+        character varying[], character varying[], double precision[]
+    ) RETURNS void
+    LANGUAGE plpgsql
+    AS $_$
+DECLARE
+    p_time alias for $1;
+    p_host alias for $2;
+    p_plugin alias for $3;
+    p_plugin_instance alias for $4;
+    p_type alias for $5;
+    p_type_instance alias for $6;
+    p_value_names alias for $7;
+    -- don't use the type info; for 'StoreRates true' it's 'gauge' anyway
+    -- p_type_names alias for $8;
+    p_values alias for $9;
+    ds_id integer;
+    i integer;
+BEGIN
+    SELECT id INTO ds_id
+        FROM identifiers
+        WHERE host = p_host
+            AND plugin = p_plugin
+            AND COALESCE(plugin_inst, '') = COALESCE(p_plugin_instance, '')
+            AND type = p_type
+            AND COALESCE(type_inst, '') = COALESCE(p_type_instance, '');
+    IF NOT FOUND THEN
+        INSERT INTO identifiers (host, plugin, plugin_inst, type, type_inst)
+            VALUES (p_host, p_plugin, p_plugin_instance, p_type, p_type_instance)
+            RETURNING id INTO ds_id;
+    END IF;
+    i := 1;
+    LOOP
+        EXIT WHEN i > array_upper(p_value_names, 1);
+        INSERT INTO values (id, tstamp, name, value)
+            VALUES (ds_id, p_time, p_value_names[i], p_values[i]);
+        i := i + 1;
+    END LOOP;
+END;
+$_$;
+