sql: Add a couple of indexes.

Remove the Builds_index from the schema, as it would have been removed in
error by the upgrade-6 upgrade.  Add a specific index on the Builds status
field, as this helps with db-get-builds queries, and add an index on the
Outputs derivation field, as this helps with the db-get-outputs part of
db-get-builds.

* src/sql/upgrade-8.sql: New file.
* src/schema.sql: Update accordingly.

src/schema.sql

@@ -85,7 +85,8 @@ CREATE TABLE Events (
 
 -- Create indexes to speed up common queries, in particular those
 -- corresponding to /api/latestbuilds and /api/queue HTTP requests.
-CREATE INDEX Builds_index ON Builds(job_name, system, status ASC, timestamp ASC, derivation, evaluation, stoptime DESC);
+CREATE INDEX Builds_status_index ON Builds (status);
+CREATE INDEX Outputs_derivation_index ON Outputs (derivation);
 CREATE INDEX Inputs_index ON Inputs(specification, name, branch);
 
 COMMIT;

src/sql/upgrade-8.sql

@@ -0,0 +1,7 @@
+BEGIN TRANSACTION;
+
+CREATE INDEX Builds_status_index ON Builds (status);
+
+CREATE INDEX Outputs_derivation_index ON Outputs (derivation);
+
+COMMIT;