Commit 0f5b7356 authored by Stan Hu's avatar Stan Hu

Fix stage index migration failing in PostgreSQL 10

As discussed in
https://www.postgresql.org/message-id/9922.1353433645%40sss.pgh.pa.us,
the PostgreSQL window function last_value may not consider the
right rows:

Note that first_value, last_value, and nth_value consider only the rows
within the "window frame", which by default contains the rows from the
start of the partition through the last peer of the current row. This is
likely to give unhelpful results for last_value and sometimes also
nth_value. You can redefine the frame by adding a suitable frame
specification (RANGE or ROWS) to the OVER clause. See Section 4.2.8 for
more information about frame specifications.

This query could be fixed by adding `RANGE BETWEEN UNBOUNDED PRECEDING
AND UNBOUNDED FOLLOWING`, but that's quite verbose. It's simpler just to
use the first_value function.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/59985
parent 74ace2a4
...@@ -21,8 +21,8 @@ module Gitlab ...@@ -21,8 +21,8 @@ module Gitlab
AND stage_idx IS NOT NULL AND stage_idx IS NOT NULL
GROUP BY stage_id, stage_idx GROUP BY stage_id, stage_idx
), indexes AS ( ), indexes AS (
SELECT DISTINCT stage_id, last_value(stage_idx) SELECT DISTINCT stage_id, first_value(stage_idx)
OVER (PARTITION BY stage_id ORDER BY freq ASC) AS index OVER (PARTITION BY stage_id ORDER BY freq DESC) AS index
FROM freqs FROM freqs
) )
......
...@@ -30,6 +30,6 @@ describe Gitlab::BackgroundMigration::MigrateStageIndex, :migration, schema: 201 ...@@ -30,6 +30,6 @@ describe Gitlab::BackgroundMigration::MigrateStageIndex, :migration, schema: 201
described_class.new.perform(100, 101) described_class.new.perform(100, 101)
expect(stages.all.pluck(:position)).to eq [2, 3] expect(stages.all.order(:id).pluck(:position)).to eq [2, 3]
end end
end end
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