PostgreSQL schema extensions for processing radacct: Data usage per period (#3258)

Provides a table, index and SP for extracting per-user data usage within
arbitrary periods using the standard radacct table entries.

diff --git a/raddb/mods-config/sql/main/postgresql/process-radacct.sql b/raddb/mods-config/sql/main/postgresql/process-radacct.sql
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+#  -*- text -*-
+#
+#  main/postgresql/process-radacct.sql -- Schema extensions for processing radacct entries
+#
+#  $Id$
+
+--  ---------------------------------
+--  - Per-user data usage over time -
+--  ---------------------------------
+--
+--  An extension to the standard schema to hold per-user data usage statistics
+--  for arbitrary periods.
+--
+--  The data_usage_by_period table is populated by periodically calling the
+--  fr_new_data_usage_period stored procedure.
+--
+--  This table can be queried in various ways to produce reports of aggregate
+--  data use over time. For example, if the fr_new_data_usage_period SP is
+--  invoked one per day just after midnight, to produce usage data with daily
+--  granularity, then a reasonably accurate monthly bandwidth summary for a
+--  given user could be obtained by queriing this table with:
+--
+--      SELECT
+--          TO_CHAR(CURRENT_TIMESTAMP, 'YYYY-Month') AS month,
+--          TRUNC(SUM(acctinputoctets)/1000/1000/1000,9) AS gb_in,
+--          TRUNC(SUM(acctoutputoctets)/1000/1000/1000,9) AS gb_out
+--      FROM
+--          data_usage_by_period
+--      WHERE
+--          username='bob' AND
+--          period_end IS NOT NULL
+--      GROUP BY
+--          month;
+--
+--           month      |    gb_in    |    gb_out
+--      ----------------+-------------+--------------
+--       2019-July      | 5.782279231 | 50.545664824
+--       2019-August    | 4.230543344 | 48.523096424
+--       2019-September | 4.847360599 | 48.631835488
+--       2019-October   | 6.456763254 | 51.686231937
+--       2019-November  | 6.362537735 | 52.385710572
+--       2019-December  | 4.301524442 | 50.762240277
+--       2020-January   | 5.436280545 | 49.067775286
+--      (7 rows)
+--
+CREATE TABLE data_usage_by_period (
+    username text,
+    period_start timestamp with time zone,
+    period_end timestamp with time zone,
+    acctinputoctets bigint,
+    acctoutputoctets bigint
+);
+ALTER TABLE data_usage_by_period ADD CONSTRAINT data_usage_by_period_pkey PRIMARY KEY (username, period_start);
+
+
+--
+--  Stored procedure that when run with some arbitrary frequency, say
+--  once per day by cron, will process the recent radacct entries to extract
+--  time-windowed data containing acct{input,output}octets ("data usage") per
+--  username, per period.
+--
+--  Each invocation will create new rows in the data_usage_by_period tables
+--  containing the data used by each user since the procedure was last invoked.
+--  The intervals do not need to be identical but care should be taken to
+--  ensure that the start/end of each period aligns well with any intended
+--  reporting intervals.
+--
+--  It can be invoked by running:
+--
+--      SELECT fr_new_data_usage_period();
+--
+--
+CREATE OR REPLACE FUNCTION fr_new_data_usage_period ()
+RETURNS void
+LANGUAGE plpgsql
+AS $$
+DECLARE v_start timestamp;
+DECLARE v_end timestamp;
+BEGIN
+
+    SELECT COALESCE(MAX(period_start), TO_TIMESTAMP(0)) INTO v_start FROM data_usage_by_period;
+    SELECT DATE_TRUNC('second',CURRENT_TIMESTAMP) INTO v_end;
+
+    --
+    -- Add the data usage for the sessions that were active in the current
+    -- period to the table. Include all sessions that finished since the start
+    -- of this period as well as those still ongoing.
+    --
+    INSERT INTO data_usage_by_period (username, period_start, period_end, acctinputoctets, acctoutputoctets)
+    SELECT *
+    FROM (
+        SELECT
+            username,
+            v_start,
+            v_end,
+            SUM(acctinputoctets) AS acctinputoctets,
+            SUM(acctoutputoctets) AS acctoutputoctets
+        FROM
+            radacct
+        WHERE
+            acctstoptime > v_start OR
+            acctstoptime IS NULL
+        GROUP BY
+            username
+    ) AS s
+    ON CONFLICT ON CONSTRAINT data_usage_by_period_pkey
+    DO UPDATE
+        SET
+            acctinputoctets = data_usage_by_period.acctinputoctets + EXCLUDED.acctinputoctets,
+            acctoutputoctets = data_usage_by_period.acctoutputoctets + EXCLUDED.acctoutputoctets,
+            period_end = v_end;
+
+    --
+    -- Create an open-ended "next period" for all ongoing sessions and carry a
+    -- negative value of their data usage to avoid double-accounting when we
+    -- process the next period. Their current data usage has already been
+    -- allocated to the current and possibly previous periods.
+    --
+    INSERT INTO data_usage_by_period (username, period_start, period_end, acctinputoctets, acctoutputoctets)
+    SELECT *
+    FROM (
+        SELECT
+            username,
+            v_end + INTERVAL '1 SECOND',
+            NULL::timestamp,
+            0 - SUM(acctinputoctets),
+            0 - SUM(acctoutputoctets)
+        FROM
+            radacct
+        WHERE
+            acctstoptime IS NULL
+        GROUP BY
+            username
+    ) AS s;
+
+END
+$$;