Mercurial > hg
view hgext/clonebundles.py @ 42044:bb271ec2fbfb
compression: introduce a `storage.revlog.zstd.level` configuration
This option control the zstd compression level used when compressing revlog
chunk. The usage of zstd for revlog compression has not graduated from
experimental yet, but we intend to fix that soon.
The option name for the compression level is more straight forward to pick, so
this changesets comes first. Having a dedicated option for each compression
engine is useful because they don't support the same range of values.
I ran the same measurement as for the zlib compression level (in the parent
changesets). The variation in repository size is stay mostly in the same (small)
range. The "read/write" performance see smallish variation, but are overall much
better than zlib. Write performance show the same tend of having better write
performance for when reaching high-end compression.
Again, we don't intend to change the default zstd compression level (currently:
3) in this series. However this is worth investigating in the future.
The Performance comparison of zlib vs zstd is quite impressive. The repository
size stay in the same range, but the performance are much better in all
situations.
Comparison summary
==================
We are looking at:
- performance range for zlib
- performance range for zstd
- comparison of default zstd (level-3) to default zlib (level 6)
- comparison of the slowest zstd time to the fastest zlib time
Read performance:
-----------------
| zlib | zstd | cmp | f2s
mercurial | 0.170159 - 0.189219 | 0.144127 - 0.149624 | 80% | 88%
pypy | 2.679217 - 2.768691 | 1.532317 - 1.705044 | 60% | 63%
netbeans | 122.477027 - 141.620281 | 72.996346 - 89.731560 | 58% | 73%
mozilla | 147.867662 - 170.572118 | 91.700995 - 105.853099 | 56% | 71%
Write performance:
------------------
| zlib | zstd | cmp | f2s
mercurial | 53.250304 - 56.2936129 | 40.877025 - 45.677286 | 75% | 86%
pypy | 460.721984 - 476.589918 | 270.545409 - 301.002219 | 63% | 65%
netbeans | 520.560316 - 715.930400 | 370.356311 - 428.329652 | 55% | 82%
mozilla | 739.803002 - 987.056093 | 505.152906 - 591.930683 | 57% | 80%
Raw data
--------
repo alg lvl .hg/store size 00manifest.d read write
mercurial zlib 1 49,402,813 5,963,475 0.170159 53.250304
mercurial zlib 6 47,197,397 5,875,730 0.182820 56.264320
mercurial zlib 9 47,121,596 5,849,781 0.189219 56.293612
mercurial zstd 1 49,737,084 5,966,355 0.144127 40.877025
mercurial zstd 3 48,961,867 5,895,208 0.146376 42.268142
mercurial zstd 5 48,200,592 5,938,676 0.149624 43.162875
mercurial zstd 10 47,833,520 5,913,353 0.145185 44.012489
mercurial zstd 15 47,314,604 5,728,679 0.147686 45.677286
mercurial zstd 20 47,330,502 5,830,539 0.145789 45.025407
mercurial zstd 22 47,330,076 5,830,539 0.143996 44.690460
pypy zlib 1 370,830,572 28,462,425 2.679217 460.721984
pypy zlib 6 340,112,317 27,648,747 2.768691 467.537158
pypy zlib 9 338,360,736 27,639,003 2.763495 476.589918
pypy zstd 1 362,377,479 27,916,214 1.532317 270.545409
pypy zstd 3 354,137,693 27,905,988 1.686718 294.951509
pypy zstd 5 342,640,043 27,655,774 1.705044 301.002219
pypy zstd 10 334,224,327 27,164,493 1.567287 285.186239
pypy zstd 15 329,000,363 26,645,965 1.637729 299.561332
pypy zstd 20 324,534,039 26,199,547 1.526813 302.149827
pypy zstd 22 324,530,595 26,198,932 1.525718 307.821218
netbeans zlib 1 1,281,847,810 165,495,457 122.477027 520.560316
netbeans zlib 6 1,205,284,353 159,161,207 139.876147 715.930400
netbeans zlib 9 1,197,135,671 155,034,586 141.620281 678.297064
netbeans zstd 1 1,259,581,737 160,840,613 72.996346 370.356311
netbeans zstd 3 1,232,978,122 157,691,551 81.622317 396.733087
netbeans zstd 5 1,208,034,075 160,246,880 83.080549 364.342626
netbeans zstd 10 1,188,624,176 156,083,417 79.323935 403.594602
netbeans zstd 15 1,176,973,589 153,859,477 89.731560 428.329652
netbeans zstd 20 1,162,958,258 151,147,535 82.842667 392.335349
netbeans zstd 22 1,162,707,029 151,150,220 82.565695 402.840655
mozilla zlib 1 2,775,497,186 298,527,987 147.867662 751.263721
mozilla zlib 6 2,596,856,420 286,597,671 170.572118 987.056093
mozilla zlib 9 2,587,542,494 287,018,264 163.622338 739.803002
mozilla zstd 1 2,723,159,348 286,617,532 91.700995 570.042751
mozilla zstd 3 2,665,055,001 286,152,013 95.240155 561.412805
mozilla zstd 5 2,607,819,817 288,060,030 101.978048 505.152906
mozilla zstd 10 2,558,761,085 283,967,648 104.113481 497.771202
mozilla zstd 15 2,526,216,060 275,581,300 105.853099 591.930683
mozilla zstd 20 2,485,114,806 266,478,859 95.268795 576.515389
mozilla zstd 22 2,484,869,080 266,456,505 94.429282 572.785537
author | Pierre-Yves David <pierre-yves.david@octobus.net> |
---|---|
date | Wed, 27 Mar 2019 18:35:59 +0100 |
parents | b4d85bc122bd |
children | 2372284d9457 |
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# This software may be used and distributed according to the terms of the # GNU General Public License version 2 or any later version. """advertise pre-generated bundles to seed clones "clonebundles" is a server-side extension used to advertise the existence of pre-generated, externally hosted bundle files to clients that are cloning so that cloning can be faster, more reliable, and require less resources on the server. "pullbundles" is a related feature for sending pre-generated bundle files to clients as part of pull operations. Cloning can be a CPU and I/O intensive operation on servers. Traditionally, the server, in response to a client's request to clone, dynamically generates a bundle containing the entire repository content and sends it to the client. There is no caching on the server and the server will have to redundantly generate the same outgoing bundle in response to each clone request. For servers with large repositories or with high clone volume, the load from clones can make scaling the server challenging and costly. This extension provides server operators the ability to offload potentially expensive clone load to an external service. Pre-generated bundles also allow using more CPU intensive compression, reducing the effective bandwidth requirements. Here's how clone bundles work: 1. A server operator establishes a mechanism for making bundle files available on a hosting service where Mercurial clients can fetch them. 2. A manifest file listing available bundle URLs and some optional metadata is added to the Mercurial repository on the server. 3. A client initiates a clone against a clone bundles aware server. 4. The client sees the server is advertising clone bundles and fetches the manifest listing available bundles. 5. The client filters and sorts the available bundles based on what it supports and prefers. 6. The client downloads and applies an available bundle from the server-specified URL. 7. The client reconnects to the original server and performs the equivalent of :hg:`pull` to retrieve all repository data not in the bundle. (The repository could have been updated between when the bundle was created and when the client started the clone.) This may use "pullbundles". Instead of the server generating full repository bundles for every clone request, it generates full bundles once and they are subsequently reused to bootstrap new clones. The server may still transfer data at clone time. However, this is only data that has been added/changed since the bundle was created. For large, established repositories, this can reduce server load for clones to less than 1% of original. Here's how pullbundles work: 1. A manifest file listing available bundles and describing the revisions is added to the Mercurial repository on the server. 2. A new-enough client informs the server that it supports partial pulls and initiates a pull. 3. If the server has pull bundles enabled and sees the client advertising partial pulls, it checks for a matching pull bundle in the manifest. A bundle matches if the format is supported by the client, the client has the required revisions already and needs something from the bundle. 4. If there is at least one matching bundle, the server sends it to the client. 5. The client applies the bundle and notices that the server reply was incomplete. It initiates another pull. To work, this extension requires the following of server operators: * Generating bundle files of repository content (typically periodically, such as once per day). * Clone bundles: A file server that clients have network access to and that Python knows how to talk to through its normal URL handling facility (typically an HTTP/HTTPS server). * A process for keeping the bundles manifest in sync with available bundle files. Strictly speaking, using a static file hosting server isn't required: a server operator could use a dynamic service for retrieving bundle data. However, static file hosting services are simple and scalable and should be sufficient for most needs. Bundle files can be generated with the :hg:`bundle` command. Typically :hg:`bundle --all` is used to produce a bundle of the entire repository. :hg:`debugcreatestreamclonebundle` can be used to produce a special *streaming clonebundle*. These are bundle files that are extremely efficient to produce and consume (read: fast). However, they are larger than traditional bundle formats and require that clients support the exact set of repository data store formats in use by the repository that created them. Typically, a newer server can serve data that is compatible with older clients. However, *streaming clone bundles* don't have this guarantee. **Server operators need to be aware that newer versions of Mercurial may produce streaming clone bundles incompatible with older Mercurial versions.** A server operator is responsible for creating a ``.hg/clonebundles.manifest`` file containing the list of available bundle files suitable for seeding clones. If this file does not exist, the repository will not advertise the existence of clone bundles when clients connect. For pull bundles, ``.hg/pullbundles.manifest`` is used. The manifest file contains a newline (\\n) delimited list of entries. Each line in this file defines an available bundle. Lines have the format: <URL> [<key>=<value>[ <key>=<value>]] That is, a URL followed by an optional, space-delimited list of key=value pairs describing additional properties of this bundle. Both keys and values are URI encoded. For pull bundles, the URL is a path under the ``.hg`` directory of the repository. Keys in UPPERCASE are reserved for use by Mercurial and are defined below. All non-uppercase keys can be used by site installations. An example use for custom properties is to use the *datacenter* attribute to define which data center a file is hosted in. Clients could then prefer a server in the data center closest to them. The following reserved keys are currently defined: BUNDLESPEC A "bundle specification" string that describes the type of the bundle. These are string values that are accepted by the "--type" argument of :hg:`bundle`. The values are parsed in strict mode, which means they must be of the "<compression>-<type>" form. See mercurial.exchange.parsebundlespec() for more details. :hg:`debugbundle --spec` can be used to print the bundle specification string for a bundle file. The output of this command can be used verbatim for the value of ``BUNDLESPEC`` (it is already escaped). Clients will automatically filter out specifications that are unknown or unsupported so they won't attempt to download something that likely won't apply. The actual value doesn't impact client behavior beyond filtering: clients will still sniff the bundle type from the header of downloaded files. **Use of this key is highly recommended**, as it allows clients to easily skip unsupported bundles. If this key is not defined, an old client may attempt to apply a bundle that it is incapable of reading. REQUIRESNI Whether Server Name Indication (SNI) is required to connect to the URL. SNI allows servers to use multiple certificates on the same IP. It is somewhat common in CDNs and other hosting providers. Older Python versions do not support SNI. Defining this attribute enables clients with older Python versions to filter this entry without experiencing an opaque SSL failure at connection time. If this is defined, it is important to advertise a non-SNI fallback URL or clients running old Python releases may not be able to clone with the clonebundles facility. Value should be "true". heads Used for pull bundles. This contains the ``;`` separated changeset hashes of the heads of the bundle content. bases Used for pull bundles. This contains the ``;`` separated changeset hashes of the roots of the bundle content. This can be skipped if the bundle was created without ``--base``. Manifests can contain multiple entries. Assuming metadata is defined, clients will filter entries from the manifest that they don't support. The remaining entries are optionally sorted by client preferences (``ui.clonebundleprefers`` config option). The client then attempts to fetch the bundle at the first URL in the remaining list. **Errors when downloading a bundle will fail the entire clone operation: clients do not automatically fall back to a traditional clone.** The reason for this is that if a server is using clone bundles, it is probably doing so because the feature is necessary to help it scale. In other words, there is an assumption that clone load will be offloaded to another service and that the Mercurial server isn't responsible for serving this clone load. If that other service experiences issues and clients start mass falling back to the original Mercurial server, the added clone load could overwhelm the server due to unexpected load and effectively take it offline. Not having clients automatically fall back to cloning from the original server mitigates this scenario. Because there is no automatic Mercurial server fallback on failure of the bundle hosting service, it is important for server operators to view the bundle hosting service as an extension of the Mercurial server in terms of availability and service level agreements: if the bundle hosting service goes down, so does the ability for clients to clone. Note: clients will see a message informing them how to bypass the clone bundles facility when a failure occurs. So server operators should prepare for some people to follow these instructions when a failure occurs, thus driving more load to the original Mercurial server when the bundle hosting service fails. """ from __future__ import absolute_import from mercurial import ( extensions, wireprotov1server, ) testedwith = 'ships-with-hg-core' def capabilities(orig, repo, proto): caps = orig(repo, proto) # Only advertise if a manifest exists. This does add some I/O to requests. # But this should be cheaper than a wasted network round trip due to # missing file. if repo.vfs.exists('clonebundles.manifest'): caps.append('clonebundles') return caps def extsetup(ui): extensions.wrapfunction(wireprotov1server, '_capabilities', capabilities)