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base repository: git/git
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compare: 08bb69d70f55cb6b44cdc6aefa7bc1d9cf4eb3f3
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  • 2 commits
  • 1 file changed
  • 1 contributor

Commits on Aug 3, 2025

  1. describe: use prio_queue 

    Replace the use a list-based priority queue whose order is maintained by
commit_list_insert_by_date() with a prio_queue.  This avoids quadratic
worst-case complexity.  And in the somewhat contrived example of
describing the 4751 commits from v2.41.0 to v2.47.0 in one go (to get a
sizable chunk of describe work with minimal ref loading overhead) it's
significantly faster:

Benchmark 1: ./git_2.50.1 describe $(git rev-list v2.41.0..v2.47.0)
  Time (mean ± σ):      1.558 s ±  0.002 s    [User: 1.492 s, System: 0.051 s]
  Range (min … max):    1.557 s …  1.562 s    10 runs

Benchmark 2: ./git describe $(git rev-list v2.41.0..v2.47.0)
  Time (mean ± σ):      1.209 s ±  0.006 s    [User: 1.143 s, System: 0.051 s]
  Range (min … max):    1.201 s …  1.219 s    10 runs

Summary
  ./git describe $(git rev-list v2.41.0..v2.47.0) ran
    1.29 ± 0.01 times faster than ./git_2.50.1 describe $(git rev-list v2.41.0..v2.47.0)

Signed-off-by: René Scharfe <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>
    @rscharfe @gitster
    rscharfe authored and gitster committed Aug 3, 2025
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  2. describe: use prio_queue_replace() 

    Optimize the sequence get+put to peek+replace to avoid one unnecessary
heap rebalance.

Do that by tracking partial get operations in a prio_queue wrapper,
struct lazy_queue, and using wrapper functions that turn get into peek
and put into replace as needed.  This is simpler than tracking the
state explicitly in the calling code.

We get a nice speedup on top of the previous patch's conversion to
prio_queue:

Benchmark 1: ./git_2.50.1 describe $(git rev-list v2.41.0..v2.47.0)
  Time (mean ± σ):      1.559 s ±  0.002 s    [User: 1.493 s, System: 0.051 s]
  Range (min … max):    1.556 s …  1.563 s    10 runs

Benchmark 2: ./git_describe_pq describe $(git rev-list v2.41.0..v2.47.0)
  Time (mean ± σ):      1.204 s ±  0.001 s    [User: 1.138 s, System: 0.051 s]
  Range (min … max):    1.202 s …  1.205 s    10 runs

Benchmark 3: ./git describe $(git rev-list v2.41.0..v2.47.0)
  Time (mean ± σ):     850.9 ms ±   1.6 ms    [User: 786.6 ms, System: 49.8 ms]
  Range (min … max):   849.1 ms … 854.1 ms    10 runs

Summary
  ./git describe $(git rev-list v2.41.0..v2.47.0) ran
    1.41 ± 0.00 times faster than ./git_describe_pq describe $(git rev-list v2.41.0..v2.47.0)
    1.83 ± 0.00 times faster than ./git_2.50.1 describe $(git rev-list v2.41.0..v2.47.0)

Signed-off-by: René Scharfe <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>
    @rscharfe @gitster
    rscharfe authored and gitster committed Aug 3, 2025
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    08bb69d View commit details
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