| Message ID | 20241108-pks-refs-optimize-migrations-v1-0-7fd37fa80e35@pks.im (mailing list archive) |
|---|---|
| Headers | show |
| Series | refs: optimize ref format migrations | expand |
Patrick Steinhardt <ps@pks.im> writes: > Hi, > > I have recently learned that ref format migrations can take a > significant amount of time in the order of minutes when migrating > millions of refs. This is probably not entirely surprising: the initial > focus for the logic to migrate ref backends was mostly focussed on > getting the basic feature working, and I didn't yet invest any time into > optimizing the code path at all. But I was still mildly surprised that > the migration of a couple million refs was taking minutes to finish. > > This patch series thus optimizes how we migrate ref formats. This is > mostly done by expanding upon the "initial transaction" semantics that > we already use for git-clone(1). These semantics allow us to assume that > the ref backend is completely empty and that there are no concurrent > writers, and thus we are free to perform certain optimizations that > wouldn't have otherwise been possible. On the one hand this allows us to > drop needless collision checks. On the other hand, it also allows us to > write regular refs directly into the "packed-refs" file when migrating > from the "reftable" backend to the "files" backend. > > This leads to some significant speedups. Migrating 1 million refs from > "files" to "reftable": > > Benchmark 1: migrate files:reftable (refcount = 1000000, revision = origin/master) > Time (mean ± σ): 4.580 s ± 0.062 s [User: 1.818 s, System: 2.746 s] > Range (min … max): 4.534 s … 4.743 s 10 runs > > Benchmark 2: migrate files:reftable (refcount = 1000000, revision = pks-refs-optimize-migrations) > Time (mean ± σ): 767.7 ms ± 9.5 ms [User: 629.2 ms, System: 126.1 ms] > Range (min … max): 755.8 ms … 786.9 ms 10 runs > > Summary > migrate files:reftable (refcount = 1000000, revision = pks-refs-optimize-migrations) ran > 5.97 ± 0.11 times faster than migrate files:reftable (refcount = 1000000, revision = origin/master) > > And migrating from "reftable" to "files: > > Benchmark 1: migrate reftable:files (refcount = 1000000, revision = origin/master) > Time (mean ± σ): 35.409 s ± 0.302 s [User: 5.061 s, System: 29.244 s] > Range (min … max): 35.055 s … 35.898 s 10 runs > > Benchmark 2: migrate reftable:files (refcount = 1000000, revision = pks-refs-optimize-migrations) > Time (mean ± σ): 855.9 ms ± 61.5 ms [User: 646.7 ms, System: 187.1 ms] > Range (min … max): 830.0 ms … 1030.3 ms 10 runs > > Summary > migrate reftable:files (refcount = 1000000, revision = pks-refs-optimize-migrations) ran > 41.37 ± 2.99 times faster than migrate reftable:files (refcount = 1000000, revision = origin/master) > > Thanks! > > Patrick > I read through the series, apart from a few small nits, the patches look good and straightforward. Thanks
On Mon, Nov 11, 2024 at 05:57:43AM -0500, karthik nayak wrote: > Patrick Steinhardt <ps@pks.im> writes: > I read through the series, apart from a few small nits, the patches > look good and straightforward. I've queued the single change to the first commit message locally, but don't think that this is sufficient reason yet to reroll the patch series, so I'll wait for additional feedback. Thanks for your review! Patrick
Hi, I have recently learned that ref format migrations can take a significant amount of time in the order of minutes when migrating millions of refs. This is probably not entirely surprising: the initial focus for the logic to migrate ref backends was mostly focussed on getting the basic feature working, and I didn't yet invest any time into optimizing the code path at all. But I was still mildly surprised that the migration of a couple million refs was taking minutes to finish. This patch series thus optimizes how we migrate ref formats. This is mostly done by expanding upon the "initial transaction" semantics that we already use for git-clone(1). These semantics allow us to assume that the ref backend is completely empty and that there are no concurrent writers, and thus we are free to perform certain optimizations that wouldn't have otherwise been possible. On the one hand this allows us to drop needless collision checks. On the other hand, it also allows us to write regular refs directly into the "packed-refs" file when migrating from the "reftable" backend to the "files" backend. This leads to some significant speedups. Migrating 1 million refs from "files" to "reftable": Benchmark 1: migrate files:reftable (refcount = 1000000, revision = origin/master) Time (mean ± σ): 4.580 s ± 0.062 s [User: 1.818 s, System: 2.746 s] Range (min … max): 4.534 s … 4.743 s 10 runs Benchmark 2: migrate files:reftable (refcount = 1000000, revision = pks-refs-optimize-migrations) Time (mean ± σ): 767.7 ms ± 9.5 ms [User: 629.2 ms, System: 126.1 ms] Range (min … max): 755.8 ms … 786.9 ms 10 runs Summary migrate files:reftable (refcount = 1000000, revision = pks-refs-optimize-migrations) ran 5.97 ± 0.11 times faster than migrate files:reftable (refcount = 1000000, revision = origin/master) And migrating from "reftable" to "files: Benchmark 1: migrate reftable:files (refcount = 1000000, revision = origin/master) Time (mean ± σ): 35.409 s ± 0.302 s [User: 5.061 s, System: 29.244 s] Range (min … max): 35.055 s … 35.898 s 10 runs Benchmark 2: migrate reftable:files (refcount = 1000000, revision = pks-refs-optimize-migrations) Time (mean ± σ): 855.9 ms ± 61.5 ms [User: 646.7 ms, System: 187.1 ms] Range (min … max): 830.0 ms … 1030.3 ms 10 runs Summary migrate reftable:files (refcount = 1000000, revision = pks-refs-optimize-migrations) ran 41.37 ± 2.99 times faster than migrate reftable:files (refcount = 1000000, revision = origin/master) Thanks! Patrick Signed-off-by: Patrick Steinhardt <ps@pks.im> --- Patrick Steinhardt (10): refs: allow passing flags when setting up a transaction refs/files: move logic to commit initial transaction refs: introduce "initial" transaction flag refs/files: support symbolic and root refs in initial transaction refs: use "initial" transaction semantics to migrate refs refs: skip collision checks in initial transactions refs: don't normalize log messages with `REF_SKIP_CREATE_REFLOG` reftable/writer: optimize allocations by using a scratch buffer reftable/block: rename `block_writer::buf` variable reftable/block: optimize allocations by using scratch buffer branch.c | 2 +- builtin/clone.c | 4 +- builtin/fast-import.c | 4 +- builtin/fetch.c | 4 +- builtin/receive-pack.c | 4 +- builtin/replace.c | 2 +- builtin/tag.c | 2 +- builtin/update-ref.c | 4 +- refs.c | 70 ++++++------- refs.h | 45 +++++---- refs/debug.c | 13 --- refs/files-backend.c | 244 +++++++++++++++++++++++++--------------------- refs/packed-backend.c | 8 -- refs/refs-internal.h | 2 +- refs/reftable-backend.c | 14 +-- reftable/block.c | 33 +++---- reftable/block.h | 9 +- reftable/writer.c | 23 +++-- reftable/writer.h | 1 + sequencer.c | 6 +- t/helper/test-ref-store.c | 2 +- t/t1460-refs-migrate.sh | 2 +- walker.c | 2 +- 23 files changed, 247 insertions(+), 253 deletions(-) --- base-commit: facbe4f633e4ad31e641f64617bc88074c659959 change-id: 20241108-pks-refs-optimize-migrations-6d0ceee4abb7 Best regards,