Schema: change sort order of history event type enum

This improves the resulting sort order when `ORDER BY event_time, event_type`
is used. `state_change` comes first as it can cause many of the other events
like trigger downtimes, remove acknowledgements and send notifications.
Similarly, `notification` comes last as any other event can result in a
notification. This will result in history events for scenarios like state
changes, triggers downtime, sends downtime start notification being sorted in
that order.

Apart from that, end events sort before the corresponding start events as any
ack/comment/downtime/flapping period should last for more than a millisecond,
therefore if there should be two events within the same millisecond, the end
event corresponds to the older period and is sorted first.

schema/mysql/schema.sql

@@ -1269,7 +1269,15 @@ CREATE TABLE history (
   flapping_history_id binary(20) DEFAULT NULL COMMENT 'flapping_history.id',
   acknowledgement_history_id binary(20) DEFAULT NULL COMMENT 'acknowledgement_history.id',
 
-  event_type enum('notification','state_change','downtime_start', 'downtime_end','comment_add','comment_remove','flapping_start','flapping_end','ack_set','ack_clear') NOT NULL,
+  -- The enum values are ordered in a way that event_type provides a meaningful sort order for history entries with
+  -- the same event_time. state_change comes first as it can cause many of the other events like trigger downtimes,
+  -- remove acknowledgements and send notifications. Similarly, notification comes last as any other event can result
+  -- in a notification. End events sort before the corresponding start events as any ack/comment/downtime/flapping
+  -- period should last for more than a millisecond, therefore, the old period ends first and then the new one starts.
+  -- The remaining types are sorted by impact and cause: comments are informative, flapping is automatic and changes
+  -- mechanics, downtimes are semi-automatic, require user action (or configuration) and change mechanics, acks are pure
+  -- user actions and change mechanics.
+  event_type enum('state_change', 'ack_clear', 'downtime_end', 'flapping_end', 'comment_remove', 'comment_add', 'flapping_start', 'downtime_start', 'ack_set', 'notification') NOT NULL,
   event_time bigint unsigned NOT NULL,
 
   PRIMARY KEY (id),

schema/mysql/upgrades/1.2.0.sql

@@ -14,3 +14,17 @@ ALTER TABLE servicegroup
     ADD INDEX idx_servicegroup_name_ci (name_ci) COMMENT 'Servicegroup list filtered using quick search',
     DROP INDEX idx_servicegroup_name,
     ADD INDEX idx_servicegroup_name (name) COMMENT 'Host/service/service group list filtered by service group name; Servicegroup detail filter';
+
+-- The following sequence of statements changes the type of history.event_type like the following statement would:
+--
+--   ALTER TABLE history MODIFY event_type enum('state_change', 'ack_clear', 'downtime_end', 'flapping_end', 'comment_remove', 'comment_add', 'flapping_start', 'downtime_start', 'ack_set', 'notification') NOT NULL;
+--
+-- It's just much faster to add a second column, copy the column using an UPDATE statement and then replace the
+-- old column with the one just generated. Table locking ensures that no other connection inserts data in the meantime.
+LOCK TABLES history WRITE;
+ALTER TABLE history ADD COLUMN event_type_new enum('state_change', 'ack_clear', 'downtime_end', 'flapping_end', 'comment_remove', 'comment_add', 'flapping_start', 'downtime_start', 'ack_set', 'notification') NOT NULL AFTER event_type;
+UPDATE history SET event_type_new = event_type;
+ALTER TABLE history
+    DROP COLUMN event_type,
+    CHANGE COLUMN event_type_new event_type enum('state_change', 'ack_clear', 'downtime_end', 'flapping_end', 'comment_remove', 'comment_add', 'flapping_start', 'downtime_start', 'ack_set', 'notification') NOT NULL;
+UNLOCK TABLES;

schema/pgsql/schema.sql

@@ -19,7 +19,16 @@ CREATE TYPE state_type AS ENUM ( 'hard', 'soft' );
 CREATE TYPE checkable_type AS ENUM ( 'host', 'service' );
 CREATE TYPE comment_type AS ENUM ( 'comment', 'ack' );
 CREATE TYPE notification_type AS ENUM ( 'downtime_start', 'downtime_end', 'downtime_removed', 'custom', 'acknowledgement', 'problem', 'recovery', 'flapping_start', 'flapping_end' );
-CREATE TYPE history_type AS ENUM ( 'notification', 'state_change', 'downtime_start', 'downtime_end', 'comment_add', 'comment_remove', 'flapping_start', 'flapping_end', 'ack_set', 'ack_clear' );
+
+-- The enum values are ordered in a way that event_type provides a meaningful sort order for history entries with
+-- the same event_time. state_change comes first as it can cause many of the other events like trigger downtimes,
+-- remove acknowledgements and send notifications. Similarly, notification comes last as any other event can result
+-- in a notification. End events sort before the corresponding start events as any ack/comment/downtime/flapping
+-- period should last for more than a millisecond, therefore, the old period ends first and then the new one starts.
+-- The remaining types are sorted by impact and cause: comments are informative, flapping is automatic and changes
+-- mechanics, downtimes are semi-automatic, require user action (or configuration) and change mechanics, acks are pure
+-- user actions and change mechanics.
+CREATE TYPE history_type AS ENUM ( 'state_change', 'ack_clear', 'downtime_end', 'flapping_end', 'comment_remove', 'comment_add', 'flapping_start', 'downtime_start', 'ack_set', 'notification' );
 
 CREATE OR REPLACE FUNCTION get_sla_ok_percent(
   in_host_id bytea20,
@@ -2040,7 +2049,7 @@ CREATE TABLE history (
   flapping_history_id bytea20 DEFAULT NULL,
   acknowledgement_history_id bytea20 DEFAULT NULL,
 
-  event_type history_type NOT NULL DEFAULT 'notification',
+  event_type history_type NOT NULL DEFAULT 'state_change',
   event_time biguint NOT NULL,
 
   CONSTRAINT pk_history PRIMARY KEY (id),

schema/pgsql/upgrades/1.2.0.sql

@@ -14,3 +14,11 @@ CREATE INDEX idx_servicegroup_name_ci ON servicegroup(name_ci);
 COMMENT ON INDEX idx_servicegroup_display_name IS 'Servicegroup list filtered/ordered by display_name';
 COMMENT ON INDEX idx_servicegroup_name_ci IS 'Servicegroup list filtered using quick search';
 COMMENT ON INDEX idx_servicegroup_name IS 'Host/service/service group list filtered by service group name; Servicegroup detail filter';
+
+ALTER TYPE history_type RENAME TO history_type_old;
+CREATE TYPE history_type AS ENUM ( 'state_change', 'ack_clear', 'downtime_end', 'flapping_end', 'comment_remove', 'comment_add', 'flapping_start', 'downtime_start', 'ack_set', 'notification' );
+ALTER TABLE history
+  ALTER COLUMN event_type DROP DEFAULT,
+  ALTER COLUMN event_type TYPE history_type USING event_type::text::history_type,
+  ALTER COLUMN event_type SET DEFAULT 'state_change'::history_type;
+DROP TYPE history_type_old;