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util: optimize cost auditing on insert...
util: optimize cost auditing on insert Calling popoldest() on insert with cost auditing enabled introduces significant overhead. The primary reason for this overhead is that popoldest() needs to walk the linked list to find the first non-empty node. When we call popoldest() within a loop, this can become quadratic. The performance impact is more pronounced on caches with large capacities. This commit effectively inlines the popoldest() call into _enforcecostlimit(). By doing so, we only do the backwards walk to find the first empty node once. However, we still may still perform this work on insert when the cache is near cost capacity. So this is only a partial performance win. $ hg perflrucachedict --size 4 --gets 1000000 --sets 1000000 --mixed 1000000 --costlimit 100 ! gets w/ cost limit ! wall 0.598737 comb 0.590000 user 0.590000 sys 0.000000 (best of 17) ! inserts w/ cost limit ! wall 1.694282 comb 1.700000 user 1.700000 sys 0.000000 (best of 6) ! wall 1.659181 comb 1.650000 user 1.650000 sys 0.000000 (best of 7) ! mixed w/ cost limit ! wall 1.157655 comb 1.150000 user 1.150000 sys 0.000000 (best of 9) ! wall 1.139955 comb 1.140000 user 1.140000 sys 0.000000 (best of 9) $ hg perflrucachedict --size 1000 --gets 1000000 --sets 1000000 --mixed 1000000 --costlimit 10000 ! gets w/ cost limit ! wall 0.598526 comb 0.600000 user 0.600000 sys 0.000000 (best of 17) ! wall 0.601993 comb 0.600000 user 0.600000 sys 0.000000 (best of 17) ! inserts w/ cost limit ! wall 37.838315 comb 37.840000 user 37.840000 sys 0.000000 (best of 3) ! wall 25.105273 comb 25.080000 user 25.080000 sys 0.000000 (best of 3) ! mixed w/ cost limit ! wall 18.060198 comb 18.060000 user 18.060000 sys 0.000000 (best of 3) ! wall 12.104470 comb 12.070000 user 12.070000 sys 0.000000 (best of 3) $ hg perflrucachedict --size 1000 --gets 1000000 --sets 1000000 --mixed 1000000 --costlimit 10000 --mixedgetfreq 90 ! gets w/ cost limit ! wall 0.600024 comb 0.600000 user 0.600000 sys 0.000000 (best of 17) ! wall 0.614439 comb 0.620000 user 0.620000 sys 0.000000 (best of 17) ! inserts w/ cost limit ! wall 37.154547 comb 37.120000 user 37.120000 sys 0.000000 (best of 3) ! wall 25.963028 comb 25.960000 user 25.960000 sys 0.000000 (best of 3) ! mixed w/ cost limit ! wall 4.381602 comb 4.380000 user 4.370000 sys 0.010000 (best of 3) ! wall 3.174256 comb 3.170000 user 3.170000 sys 0.000000 (best of 4) Differential Revision: https://phab.mercurial-scm.org/D4504

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bundlespec.txt
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Mercurial supports generating standalone "bundle" files that hold repository
data. These "bundles" are typically saved locally and used later or exchanged
between different repositories, possibly on different machines. Example
commands using bundles are :hg:`bundle` and :hg:`unbundle`.
Generation of bundle files is controlled by a "bundle specification"
("bundlespec") string. This string tells the bundle generation process how
to create the bundle.
A "bundlespec" string is composed of the following elements:
type
A string denoting the bundle format to use.
compression
Denotes the compression engine to use compressing the raw bundle data.
parameters
Arbitrary key-value parameters to further control bundle generation.
A "bundlespec" string has the following formats:
<type>
The literal bundle format string is used.
<compression>-<type>
The compression engine and format are delimited by a hyphen (``-``).
Optional parameters follow the ``<type>``. Parameters are URI escaped
``key=value`` pairs. Each pair is delimited by a semicolon (``;``). The
first parameter begins after a ``;`` immediately following the ``<type>``
value.
Available Types
===============
The following bundle <type> strings are available:
v1
Produces a legacy "changegroup" version 1 bundle.
This format is compatible with nearly all Mercurial clients because it is
the oldest. However, it has some limitations, which is why it is no longer
the default for new repositories.
``v1`` bundles can be used with modern repositories using the "generaldelta"
storage format. However, it may take longer to produce the bundle and the
resulting bundle may be significantly larger than a ``v2`` bundle.
``v1`` bundles can only use the ``gzip``, ``bzip2``, and ``none`` compression
formats.
v2
Produces a version 2 bundle.
Version 2 bundles are an extensible format that can store additional
repository data (such as bookmarks and phases information) and they can
store data more efficiently, resulting in smaller bundles.
Version 2 bundles can also use modern compression engines, such as
``zstd``, making them faster to compress and often smaller.
Available Compression Engines
=============================
The following bundle <compression> engines can be used:
.. bundlecompressionmarker
Examples
========
``v2``
Produce a ``v2`` bundle using default options, including compression.
``none-v1``
Produce a ``v1`` bundle with no compression.
``zstd-v2``
Produce a ``v2`` bundle with zstandard compression using default
settings.
``zstd-v1``
This errors because ``zstd`` is not supported for ``v1`` types.