Page MenuHomePhabricator

copies: move from a copy on branchpoint to a copy on write approach
ClosedPublic

Authored by marmoute on Wed, Oct 16, 7:48 PM.

Details

Summary

Before this changes, any branch points results in a copy of the dictionary containing the
copy information. This can be very costly for branchy history with few rename
information. Instead, we take a "copy on write" approach. Copying the input data
only when we are about to update them.

In practice we where already doing the copying in half of these case (because
_chain makes a copy), so we don't add a significant cost here even in the
linear case. However the speed up in branchy case is very significant. Here are
some timing on the pypy repository.

revision: large amount; added files: large amount; rename small amount; c3b14617fbd7 9ba6ab77fd29
before: ! wall 1.399863 comb 1.400000 user 1.370000 sys 0.030000 (median of 10)
after: ! wall 0.766453 comb 0.770000 user 0.750000 sys 0.020000 (median of 11)
revision: large amount; added files: small amount; rename small amount; c3b14617fbd7 f650a9b140d2
before: ! wall 1.876748 comb 1.890000 user 1.870000 sys 0.020000 (median of 10)
after: ! wall 1.167223 comb 1.170000 user 1.150000 sys 0.020000 (median of 10)
revision: large amount; added files: large amount; rename large amount; 08ea3258278e d9fa043f30c0
before: ! wall 0.242457 comb 0.240000 user 0.240000 sys 0.000000 (median of 39)
after: ! wall 0.211476 comb 0.210000 user 0.210000 sys 0.000000 (median of 45)
revision: small amount; added files: large amount; rename large amount; df6f7a526b60 a83dc6a2d56f
before: ! wall 0.013193 comb 0.020000 user 0.020000 sys 0.000000 (median of 224)
after: ! wall 0.013290 comb 0.010000 user 0.010000 sys 0.000000 (median of 222)
revision: small amount; added files: large amount; rename small amount; 4aa4e1f8e19a 169138063d63
before: ! wall 0.001673 comb 0.000000 user 0.000000 sys 0.000000 (median of 1000)
after: ! wall 0.001677 comb 0.000000 user 0.000000 sys 0.000000 (median of 1000)
revision: small amount; added files: small amount; rename small amount; 4bc173b045a6 964879152e2e
before: ! wall 0.000119 comb 0.000000 user 0.000000 sys 0.000000 (median of 8023)
after: ! wall 0.000119 comb 0.000000 user 0.000000 sys 0.000000 (median of 7997)
revision: medium amount; added files: large amount; rename medium amount; c95f1ced15f2 2c68e87c3efe
before: ! wall 0.201898 comb 0.210000 user 0.200000 sys 0.010000 (median of 48)
after: ! wall 0.167415 comb 0.170000 user 0.160000 sys 0.010000 (median of 58)
revision: medium amount; added files: medium amount; rename small amount; d343da0c55a8 d7746d32bf9d
before: ! wall 0.036820 comb 0.040000 user 0.040000 sys 0.000000 (median of 100)
after: ! wall 0.035797 comb 0.040000 user 0.040000 sys 0.000000 (median of 100)

The extra cost in the linear case can be reclaimed later with some extra logic.

Diff Detail

Repository
rHG Mercurial
Lint
Automatic diff as part of commit; lint not applicable.
Unit
Automatic diff as part of commit; unit tests not applicable.

Event Timeline

marmoute created this revision.Wed, Oct 16, 7:48 PM
marmoute updated this revision to Diff 17331.Thu, Oct 17, 7:46 PM
This revision was not accepted when it landed; it landed in state Needs Review.
This revision was automatically updated to reflect the committed changes.