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util: lower water mark when removing nodes after cost limit reached...
util: lower water mark when removing nodes after cost limit reached See the inline comment for the reasoning here. This is a pretty common strategy for garbage collectors, other cache-like primtives. The performance impact is substantial: $ hg perflrucachedict --size 4 --gets 1000000 --sets 1000000 --mixed 1000000 --costlimit 100 ! inserts w/ cost limit ! wall 1.659181 comb 1.650000 user 1.650000 sys 0.000000 (best of 7) ! wall 1.722122 comb 1.720000 user 1.720000 sys 0.000000 (best of 6) ! mixed w/ cost limit ! wall 1.139955 comb 1.140000 user 1.140000 sys 0.000000 (best of 9) ! wall 1.182513 comb 1.180000 user 1.180000 sys 0.000000 (best of 9) $ hg perflrucachedict --size 1000 --gets 1000000 --sets 1000000 --mixed 1000000 --costlimit 10000 ! inserts ! wall 0.679546 comb 0.680000 user 0.680000 sys 0.000000 (best of 15) ! sets ! wall 0.825147 comb 0.830000 user 0.830000 sys 0.000000 (best of 13) ! inserts w/ cost limit ! wall 25.105273 comb 25.080000 user 25.080000 sys 0.000000 (best of 3) ! wall 1.724397 comb 1.720000 user 1.720000 sys 0.000000 (best of 6) ! mixed ! wall 0.807096 comb 0.810000 user 0.810000 sys 0.000000 (best of 13) ! mixed w/ cost limit ! wall 12.104470 comb 12.070000 user 12.070000 sys 0.000000 (best of 3) ! wall 1.190563 comb 1.190000 user 1.190000 sys 0.000000 (best of 9) $ hg perflrucachedict --size 1000 --gets 1000000 --sets 1000000 --mixed 1000000 --costlimit 10000 --mixedgetfreq 90 ! inserts ! wall 0.711177 comb 0.710000 user 0.710000 sys 0.000000 (best of 14) ! sets ! wall 0.846992 comb 0.850000 user 0.850000 sys 0.000000 (best of 12) ! inserts w/ cost limit ! wall 25.963028 comb 25.960000 user 25.960000 sys 0.000000 (best of 3) ! wall 2.184311 comb 2.180000 user 2.180000 sys 0.000000 (best of 5) ! mixed ! wall 0.728256 comb 0.730000 user 0.730000 sys 0.000000 (best of 14) ! mixed w/ cost limit ! wall 3.174256 comb 3.170000 user 3.170000 sys 0.000000 (best of 4) ! wall 0.773186 comb 0.770000 user 0.770000 sys 0.000000 (best of 13) $ hg perflrucachedict --size 100000 --gets 1000000 --sets 1000000 --mixed 1000000 --mixedgetfreq 90 --costlimit 5000000 ! gets ! wall 1.191368 comb 1.190000 user 1.190000 sys 0.000000 (best of 9) ! wall 1.195304 comb 1.190000 user 1.190000 sys 0.000000 (best of 9) ! inserts ! wall 0.950995 comb 0.950000 user 0.950000 sys 0.000000 (best of 11) ! inserts w/ cost limit ! wall 1.589732 comb 1.590000 user 1.590000 sys 0.000000 (best of 7) ! sets ! wall 1.094941 comb 1.100000 user 1.090000 sys 0.010000 (best of 9) ! mixed ! wall 0.936420 comb 0.940000 user 0.930000 sys 0.010000 (best of 10) ! mixed w/ cost limit ! wall 0.882780 comb 0.870000 user 0.870000 sys 0.000000 (best of 11) This puts us ~2x slower than caches without cost accounting. And for read-heavy workloads (the prime use cases for caches), performance is nearly identical. In the worst case (pure write workloads with cost accounting enabled), we're looking at ~1.5us per insert on large caches. That seems "fast enough." Differential Revision: https://phab.mercurial-scm.org/D4505

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phases.txt
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What are phases?
================
Phases are a system for tracking which changesets have been or should
be shared. This helps prevent common mistakes when modifying history
(for instance, with the mq or rebase extensions).
Each changeset in a repository is in one of the following phases:
- public : changeset is visible on a public server
- draft : changeset is not yet published
- secret : changeset should not be pushed, pulled, or cloned
These phases are ordered (public < draft < secret) and no changeset
can be in a lower phase than its ancestors. For instance, if a
changeset is public, all its ancestors are also public. Lastly,
changeset phases should only be changed towards the public phase.
How are phases managed?
=======================
For the most part, phases should work transparently. By default, a
changeset is created in the draft phase and is moved into the public
phase when it is pushed to another repository.
Once changesets become public, extensions like mq and rebase will
refuse to operate on them to prevent creating duplicate changesets.
Phases can also be manually manipulated with the :hg:`phase` command
if needed. See :hg:`help -v phase` for examples.
To make your commits secret by default, put this in your
configuration file::
[phases]
new-commit = secret
Phases and servers
==================
Normally, all servers are ``publishing`` by default. This means::
- all draft changesets that are pulled or cloned appear in phase
public on the client
- all draft changesets that are pushed appear as public on both
client and server
- secret changesets are neither pushed, pulled, or cloned
.. note::
Pulling a draft changeset from a publishing server does not mark it
as public on the server side due to the read-only nature of pull.
Sometimes it may be desirable to push and pull changesets in the draft
phase to share unfinished work. This can be done by setting a
repository to disable publishing in its configuration file::
[phases]
publish = False
See :hg:`help config` for more information on configuration files.
.. note::
Servers running older versions of Mercurial are treated as
publishing.
.. note::
Changesets in secret phase are not exchanged with the server. This
applies to their content: file names, file contents, and changeset
metadata. For technical reasons, the identifier (e.g. d825e4025e39)
of the secret changeset may be communicated to the server.
Examples
========
- list changesets in draft or secret phase::
hg log -r "not public()"
- change all secret changesets to draft::
hg phase --draft "secret()"
- forcibly move the current changeset and descendants from public to draft::
hg phase --force --draft .
- show a list of changeset revisions and each corresponding phase::
hg log --template "{rev} {phase}\n"
- resynchronize draft changesets relative to a remote repository::
hg phase -fd "outgoing(URL)"
See :hg:`help phase` for more information on manually manipulating phases.