snapshot: search for unrelated but reusable full-snapshot # New Strategy Step: Reusing Snapshot Outside Of Parents' Chain. If no suitable bases were found in the parent's chains, see if we could reuse a full snapshot not directly related to the current revision. Such search can be expensive, so we only search for snapshots appended to the revlog *after* the bases used by the parents of the current revision (the one we just tested). We assume the parent's bases were created because the previous snapshots were unsuitable, so there are low odds they would be useful now. This search gives a chance to reuse a delta chain unrelated to the current revision. Without this re-use, topological branches would keep reopening new full chains. Creating more and more snapshots as the repository grow. In repositories with many topological branches, the lack of delta reuse can create too many snapshots reducing overall compression to nothing. This results in a very large repository and other usability issues. For now, we still focus on creating level-1 snapshots. However, this principle will play a large part in how we avoid snapshot explosion once we have more snapshot levels. # Effects On The Test Repository In the test repository we created, we can see the beneficial effect of such reuse. We need very few level-0 snapshots and the overall revlog size has decreased. The `hg debugrevlog` call, show a "lvl-2" snapshot. It comes from the existing delta logic using the `prev` revision (revlog's tip) as the base. In this specific case, it turns out the tip was a level-1 snapshot. This is a coincidence that can be ignored. Finding and testing against all these unrelated snapshots can have a performance impact at write time. We currently focus on building good deltas chain we build. Performance concern will be dealt with later in another series.

snapshot: try intermediate snapshot against parents' base # Regarding The Series Started By This Changeset This is the first changesets of a group adjusting delta chain strategy to build a useful chain of intermediate snapshots. The series will introduce a full strategy to produce chains of multiple snapshots on top of which a "usual" delta chain will be built. That strategy will have multiple steps to maximize snapshot reuse, avoiding pathological cases and improving overall compression in very branchy repositories. An important property of sparse-revlog using such snapshot-chain is that they can use very short delta chain without problematic impact on the resulting compression. Shorter delta chains are important to achieve good performance. To make each step clear, we'll introduce them one by one. See the end of this series for full details. # Regarding This Changeset Before this change, if we cannot store the current revision as a delta against a "simple" candidate (p1, p2, prev), we created a new level-0 snapshot (also called full snapshot). As the first step, we introduce a simple strategy: try an intermediate level-1 snapshot against the chain base of the "current revision" parents. The "current revision" is the one we are currently trying to store in the revlog, triggering this search for a good delta base. The first item in the chain is always a level-0 snapshot. # Effect On The Test Repository We can already see the effect on the test-repository. Most of the snapshots have shifted from level 0 to level 1. The overall size has slightly decreased. (However, keep in mind that this repository only emulates real data) # Regarding Statistic The current series focuses on improving the chain built. Improving the performance of this logic will be done as a second step. Sparse-revlog is still experimental and disabled by default. We'll provide more statistic about resulting size and delta chain at the end of this series.

sparse-revlog: add a test checking revlog deltas for a churning file The test repository contains 5000 revisions and is therefore slow to build: five minutes with CHG, over fifteen minutes without. It is too slow to build during the test. Bundling all content produce a sizeable result, 20BM, too large to be committed. Instead, we commit a script to build the expected bundle and the test checks if the bundle is available. Any run of the script will produce the same repository content, using resulting in the same hashes. Using smaller repositories was tried, however, it misses most of the cases we are planning to improve. Having them in a 5000 repository is already nice, we usually see these case in repositories in the order of magnitude of one million revisions. This test will be very useful to check various changes strategy for building delta to store in a sparse-revlog. In this series we will focus our attention on the following metrics: The ones that will impact the final storage performance (size, space): * size of the revlog data file (".hg/store/data/*.d") * chain length info The ones that describe the deltas patterns: * number of snapshot revision (and their level) * size taken by snapshot revision (and their level)

tests: add a `tests/artifacts/` directory That directory is meant to cache large items used by tests that are slow to generate. See 'PURPOSE' file for details and next changesets for a first user.

verify: make output less confusing (issue5924) output before: "500 files, 2035 changesets, 2622 total revisions" output after: "checked 2035 changesets with 2622 changes to 500 files" new one was suggested in the comments inside the issue. Differential Revision: https://phab.mercurial-scm.org/D4476

revlog: clarify the comment attached to delta reuse The previous version was a bit complicated and referred to a deprecated configuration option.

revlog: drop duplicated code This code probably got duplicated by a rebase/evolve conflict. We drop the extra copy, the other copy is right below. This had no real effects since other logic ensure that we never test the same revision twice.

wireprotov2peer: properly format errors formatrichmessage() expects an iterable containing dicts with well-defined keys. We were passing in something else. This caused an exception. Change the code to call formatrichmessage() with the proper argument. And add a TODO to potentially emit the proper data structure from the server in the first place. Differential Revision: https://phab.mercurial-scm.org/D4441

wireprotov2peer: report exceptions in frame handling against request future Otherwise the future may never resolve, which could cause deadlock. Differential Revision: https://phab.mercurial-scm.org/D4440

httppeer: use util.readexactly() to abort on incomplete responses Plain resp.read(n) may not return exactly n bytes when we need, and to detect such cases before trying to interpret whatever has been read, we can use util.readexactly(), which raises an Abort when stream ends unexpectedly. In the first case here, readexactly() prevents a traceback with struct.error, in the second it avoids looking for invalid compression engines. In this test case, _wraphttpresponse doesn't catch the problem (presumably because it doesn't know transfer encoding), and the code continues reading the response until it gets to compression engine data. Maybe there should be checks before the execution gets there, but I'm not sure where (httplib?)

httppeer: calculate total expected bytes correctly User-facing error messages that handled httplib.IncompleteRead errors in Mercurial used to look like this: abort: HTTP request error (incomplete response; expected 3 bytes got 1) But the errors that are being handled underneath the UI look like this: IncompleteRead(1 bytes read, 3 more expected) I.e. the error actually counts total number of expected bytes minus bytes already received. Before, users could see weird messages like "expected 10 bytes got 10", while in reality httplib expected 10 _more_ bytes (20 in total).

lazyancestors: reuse __iter__ implementation in __contains__ There was a comment in the code that said "Trying to do both __iter__ and __contains__ using the same visit heap and seen set is complex enough that it slows down both. Keep them separate.". However, it seems easy and efficient to make __contains__ keep an iterator across calls. I couldn't measure any slowdown from `hg bundle --all` (which seem to call lazyancestors.__contains__ frequently). Differential Revision: https://phab.mercurial-scm.org/D4508

lazyancestors: extract __iter__ to free function The next patch will keep a reference to the returned iterator in a field, which would otherwise result in a reference cycle. Differential Revision: https://phab.mercurial-scm.org/D4517

phase: report number of non-public changeset alongside the new range When interacting with non-publishing repository or bundle, it is useful to have some information about the phase of the changeset we just pulled. This changeset updates the "new changesets MIN:MAX" output to also includes phases information for non-public changesets. Displaying extra data about non-public changesets means the output for exchange with publishing repository (the default) is unaffected.

tests: disable test-nointerrupt on Windows Per the followup discussion[1]. proc.send_signal(INT) in timeout.py raises a ValueError because of an unsupported signal. I don't like missing test coverage for this on Windows. But this is the last test failing on Windows, and red all the time hides new failures. [1] https://phab.mercurial-scm.org/D3716

tests: conditionalize an error message about unlinking a non empty directory The message on Windows comes from win32.unlink(). It looks like os.unlink() on posix platforms is a simple call to unlink(3), which turns into unlinkat(2). Since there's a comment in one of the tests that the message should be improved, I don't think it's worth adding a check in win32.unlink() to see if it's empty, if that function is always going to fail on a directory. (It seems like the POSIX spec allows unlinking directories though.)

ancestors: add nullrev to set from the beginning Differential Revision: https://phab.mercurial-scm.org/D4507

ancestor: filter out initial revisions lower than stoprev

ancestor: add test showing inconsistency between __iter__ and __contains__

ancestors: ensure a consistent order even in the "inclusive" case It seems odds to first issue the "source" revs and then the other ancestors. In addition, doing so can break the other contract of always issuing a child before its parent. We update the code to apply the same logic to all yielded revision. No tests break so we seem in the clear except where we explicitly test the order.

ancestors: actually iterate over ancestors in topological order (issue5979) This code previously used a dequeue logic, the first ancestors seen were the first ancestors to be emitted. In branching/merging situations, it can result in ancestors being yielded before their descendants, breaking the object contract. We got affected by this issue while working on the copy tracing code. At about the same time, Axel Hecht <axel@mozilla.com> reported the issue and provided the test case used in this changeset. Thanks Axel. Running `hg perfancestors` does not show a significant difference between the old and the new version.

doc: use modern import style in runrst

hgweb: do not audit URL path as working-directory path Since hgweb is an interface to repository data, we don't need to prohibit any paths conflicting within the filesystem. Still an access to working files is audited by filectx.

hgweb: map Abort to 403 error to report inaccessible path for example Abort is so common in our codebase. We could instead introduce a dedicated type for path auditing errors, but we'll probably have to catch error.Abort anyway. As you can see, an abort message may include a full path to the repository, which might be considered information leak. If that matters, we should hide the message and send it to the server log instead.

hgweb: add error template to json so it won't crash

hgweb: show shortlog by default in json output (issue5978)

merge with stable

tests: improve the widening testing in test-narrow-widen* Before this patch, we are testing `hg tracked --addinclude` by adding a command which is not introduced in the changesets till now. If you closely look at the tests, wider/f was introduced on the server after the narrow clone was done and extending the existing clone to include wider/f does not make sense. We should test extending a file which exists. Differential Revision: https://phab.mercurial-scm.org/D4452

narrow: use util.readfile() and improve error message using --narrowspec This patch improves the error message and uses util.readfile() for reading narrowspecs file while cloning. Differential Revision: https://phab.mercurial-scm.org/D4462

merge: use vfs methods for I/O All I/O is supposed to be performed via vfs instances so filesystems can be abstracted. The previous commit ported the old code in purge, which didn't go through the vfs layer. This commit ports the purge code to use the vfs layer. The vfs layer didn't have a method to remove a single directory, so it was added as part of implementing this. Differential Revision: https://phab.mercurial-scm.org/D4478