Change build order to HEAD-revisions then revision-time.

[Mark Potter <mpotter@…>]

Originally a part of #556 (comment:4, comment:5, comment:7), but with a simpler prescribed solution.

From what I can tell currently builds are performed in the order: Revision time, most recent first.

Scenario

This is a real example.

• "Build all revisions" is checked.
• There where 5 active branches.
• Each branch caused the build of between 21 and 25 targets.

Day 1 (4/28)

• 10:10 a change was made to the target-branch. Prior to this the build system was idle.
• by 18:00
  • 13 additional revisions were made to other branches.
  • 251 builds from these other more resent revisions still remain to be built.
  • Only 9 of the 21 builds from the target-revision had been built.
• System continues building through the night, but no other target-revision builds are made.

Day 2 (4/29)

• 04:59 the HEAD of all of the other branches had completed building.
  • However there are still 135 builds from other more resent revisions.
• 11:43 another revision was made to another branch.
  • Thus there was 6:44 where all the other recipes had finished their HEADs, but the target-revision still did not get any more building. There were 74 builds still remaining from the more resent revisions.
• by 18:00
  • 4 total additional revisions where made to other branches.
  • 144 builds from the more resent revisions still remain to be built.
• System continues building through the night, but no other target-revision builds are made.

Day 3 (4/30)

• 01:05 the HEAD of all of the other branches has completed building.
  • However there are still 118 builds from other more resent revisions.
• 09:43 another revision was made to another branch.
  • Thus there was 8:38 where all the other recipes had finished their HEADs, but the target-revision still did not get any more builds. There were 66 builds still remaining from the more resent revisions.
• 11:40 another revision was made to the target-branch.
  • Thus the original revision is no longer the HEAD of the target-branch.
• 11:31 First build from this new revision completes.
• 15:07 Fourteenth build from this new revision completes.
• 15:17 and 15:19 Two more revisions to another branch are made.
• 18:05 Twenty-first and last build from the new target-branch revision completes.

Desired Change

The HEAD of any recipe should take precedence over back-building.

Change the order in which builds are performed from revision-time to HEAD-revisions then revision-time.

[Mark Potter <mpotter@…>]

Replying to Mark Potter <mpotter@…>:

Change the order in which builds are performed from revision-time to HEAD-revisions then revision-time.

Questions:

• Where is this decision made? Is it here​, or elsewhere?
• Is there any existing code for deciding if a revision is the HEAD revision or any thoughts on how one might approach this? I can think of some SQL to do it, but there may be a better approach.

[Mark Potter <mpotter@…>]

Replying to Mark Potter <mpotter@…>:

Questions:

• Where is this decision made? Is it here​, or elsewhere?

Ah, found it: queue.py get_build_for_slave​.