• Yorick Peterse's avatar
    Update composite pipelines index to include "id" · aafe5c12
    Yorick Peterse authored
    This updates the composite index on ci_pipelines (project_id, ref,
    status) to also include the "id" column at the end. Adding this column
    to the index drastically improves the performance of queries used for
    getting the latest pipeline for a particular branch. For example, on
    project dashboards we'll run a query like the following:
        SELECT ci_pipelines.*
        FROM ci_pipelines
        WHERE ci_pipelines.project_id = 13083
        AND ci_pipelines.ref = 'master'
        AND ci_pipelines.status = 'success'
        ORDER BY ci_pipelines.id DESC
        LIMIT 1;
        Limit  (cost=0.43..58.88 rows=1 width=224) (actual time=26.956..26.956 rows=1 loops=1)
          Buffers: shared hit=6544 dirtied=16
          ->  Index Scan Backward using ci_pipelines_pkey on ci_pipelines  (cost=0.43..830922.89 rows=14216 width=224) (actual time=26.954..26.954 rows=1 loops=1)
                Filter: ((project_id = 13083) AND ((ref)::text = 'master'::text) AND ((status)::text = 'success'::text))
                Rows Removed by Filter: 6476
                Buffers: shared hit=6544 dirtied=16
        Planning time: 1.484 ms
        Execution time: 27.000 ms
    Because of the lack of "id" in the index we end up scanning over the
    primary key index, then applying a filter to filter out any remaining
    rows. The more pipelines a GitLab instance has the slower this will get.
    By adding "id" to the mentioned composite index we can change the above
    plan into the following:
        Limit  (cost=0.56..2.01 rows=1 width=224) (actual time=0.034..0.034 rows=1 loops=1)
          Buffers: shared hit=5
          ->  Index Scan Backward using yorick_test on ci_pipelines  (cost=0.56..16326.37 rows=11243 width=224) (actual time=0.033..0.033 rows=1 loops=1)
                Index Cond: ((project_id = 13083) AND ((ref)::text = 'master'::text) AND ((status)::text = 'success'::text))
                Buffers: shared hit=5
        Planning time: 0.695 ms
        Execution time: 0.061 ms
    This in turn leads to a best-case improvement of roughly 25
    milliseconds, give or take a millisecond or two.
20171121144800_ci_pipelines_index_on_project_id_ref_status_id.rb 928 Bytes