Mercurial > hg
view tests/drawdag.py @ 40326:fed697fa1734
sqlitestore: file storage backend using SQLite
This commit provides an extension which uses SQLite to store file
data (as opposed to revlogs).
As the inline documentation describes, there are still several
aspects to the extension that are incomplete. But it's a start.
The extension does support basic clone, checkout, and commit
workflows, which makes it suitable for simple use cases.
One notable missing feature is support for "bundlerepos." This is
probably responsible for the most test failures when the extension
is activated as part of the test suite.
All revision data is stored in SQLite. Data is stored as zstd
compressed chunks (default if zstd is available), zlib compressed
chunks (default if zstd is not available), or raw chunks (if
configured or if a compressed delta is not smaller than the raw
delta). This makes things very similar to revlogs.
Unlike revlogs, the extension doesn't yet enforce a limit on delta
chain length. This is an obvious limitation and should be addressed.
This is somewhat mitigated by the use of zstd, which is much faster
than zlib to decompress.
There is a dedicated table for storing deltas. Deltas are stored
by the SHA-1 hash of their uncompressed content. The "fileindex" table
has columns that reference the delta for each revision and the base
delta that delta should be applied against. A recursive SQL query
is used to resolve the delta chain along with the delta data.
By storing deltas by hash, we are able to de-duplicate delta storage!
With revlogs, the same deltas in different revlogs would result in
duplicate storage of that delta. In this scheme, inserting the
duplicate delta is a no-op and delta chains simply reference the
existing delta.
When initially implementing this extension, I did not have
content-indexed deltas and deltas could be duplicated across files
(just like revlogs). When I implemented content-indexed deltas, the
size of the SQLite database for a full clone of mozilla-unified
dropped:
before: 2,554,261,504 bytes
after: 2,488,754,176 bytes
Surprisingly, this is still larger than the bytes size of revlog
files:
revlog files: 2,104,861,230 bytes
du -b: 2,254,381,614
I would have expected storage to be smaller since we're not limiting
delta chain length and since we're using zstd instead of zlib. I
suspect the SQLite indexes and per-column overhead account for the
bulk of the differences. (Keep in mind that revlog uses a 64-byte
packed struct for revision index data and deltas are stored without
padding. Aside from the 12 unused bytes in the 32 byte node field,
revlogs are pretty efficient.) Another source of overhead is file
name storage. With revlogs, file names are stored in the filesystem.
But with SQLite, we need to store file names in the database. This is
roughly equivalent to the size of the fncache file, which for the
mozilla-unified repository is ~34MB.
Since the SQLite database isn't append-only and since delta chains
can reference any delta, this opens some interesting possibilities.
For example, we could store deltas in reverse, such that fulltexts
are stored for newer revisions and deltas are applied to reconstruct
older revisions. This is likely a more optimal storage strategy for
version control, as new data tends to be more frequently accessed
than old data. We would obviously need wire protocol support for
transferring revision data from newest to oldest. And we would
probably need some kind of mechanism for "re-encoding" stores. But
it should be doable.
This extension is very much experimental quality. There are a handful
of features that don't work. It probably isn't suitable for day-to-day
use. But it could be used in limited cases (e.g. read-only checkouts
like in CI). And it is also a good proving ground for alternate
storage backends. As we continue to define interfaces for all things
storage, it will be useful to have a viable alternate storage backend
to see how things shake out in practice.
test-storage.py passes on Python 2 and introduces no new test failures on
Python 3. Having the storage-level unit tests has proved to be insanely
useful when developing this extension. Those tests caught numerous bugs
during development and I'm convinced this style of testing is the way
forward for ensuring alternate storage backends work as intended. Of
course, test coverage isn't close to what it needs to be. But it is
a start. And what coverage we have gives me confidence that basic store
functionality is implemented properly.
Differential Revision: https://phab.mercurial-scm.org/D4928
author | Gregory Szorc <gregory.szorc@gmail.com> |
---|---|
date | Tue, 09 Oct 2018 08:50:13 -0700 |
parents | 9a813e4c8406 |
children | 8d4ee2d9ffb8 |
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# drawdag.py - convert ASCII revision DAG to actual changesets # # Copyright 2016 Facebook, Inc. # # This software may be used and distributed according to the terms of the # GNU General Public License version 2 or any later version. """ create changesets from an ASCII graph for testing purpose. For example, given the following input:: c d |/ b | a 4 changesets and 4 local tags will be created. `hg log -G -T "{rev} {desc} (tag: {tags})"` will output:: o 3 d (tag: d tip) | | o 2 c (tag: c) |/ o 1 b (tag: b) | o 0 a (tag: a) For root nodes (nodes without parents) in the graph, they can be revsets pointing to existing nodes. The ASCII graph could also have disconnected components with same names referring to the same changeset. Therefore, given the repo having the 4 changesets (and tags) above, with the following ASCII graph as input:: foo bar bar foo | / | | ancestor(c,d) a baz The result (`hg log -G -T "{desc}"`) will look like:: o foo |\ +---o bar | | | | o | baz | / +---o d | | +---o c | | o | b |/ o a Note that if you take the above `hg log` output directly as input. It will work as expected - the result would be an isomorphic graph:: o foo |\ | | o d | |/ | | o c | |/ | | o bar | |/| | o | b | |/ o / baz / o a This is because 'o' is specially handled in the input: instead of using 'o' as the node name, the word to the right will be used. Some special comments could have side effects: - Create obsmarkers # replace: A -> B -> C -> D # chained 1 to 1 replacements # split: A -> B, C # 1 to many # prune: A, B, C # many to nothing """ from __future__ import absolute_import, print_function import collections import itertools import re from mercurial.i18n import _ from mercurial import ( context, error, node, obsolete, pycompat, registrar, scmutil, tags as tagsmod, ) cmdtable = {} command = registrar.command(cmdtable) _pipechars = b'\\/+-|' _nonpipechars = b''.join(pycompat.bytechr(i) for i in range(33, 127) if pycompat.bytechr(i) not in _pipechars) def _isname(ch): """char -> bool. return True if ch looks like part of a name, False otherwise""" return ch in _nonpipechars def _parseasciigraph(text): r"""str -> {str : [str]}. convert the ASCII graph to edges >>> import pprint >>> pprint.pprint({pycompat.sysstr(k): [pycompat.sysstr(vv) for vv in v] ... for k, v in _parseasciigraph(br''' ... G ... | ... I D C F # split: B -> E, F, G ... \ \| | # replace: C -> D -> H ... H B E # prune: F, I ... \|/ ... A ... ''').items()}) {'A': [], 'B': ['A'], 'C': ['B'], 'D': ['B'], 'E': ['A'], 'F': ['E'], 'G': ['F'], 'H': ['A'], 'I': ['H']} >>> pprint.pprint({pycompat.sysstr(k): [pycompat.sysstr(vv) for vv in v] ... for k, v in _parseasciigraph(br''' ... o foo ... |\ ... +---o bar ... | | | ... | o | baz ... | / ... +---o d ... | | ... +---o c ... | | ... o | b ... |/ ... o a ... ''').items()}) {'a': [], 'b': ['a'], 'bar': ['b', 'a'], 'baz': [], 'c': ['b'], 'd': ['b'], 'foo': ['baz', 'b']} """ lines = text.splitlines() edges = collections.defaultdict(list) # {node: []} def get(y, x): """(int, int) -> char. give a coordinate, return the char. return a space for anything out of range""" if x < 0 or y < 0: return b' ' try: return lines[y][x:x + 1] or b' ' except IndexError: return b' ' def getname(y, x): """(int, int) -> str. like get(y, x) but concatenate left and right parts. if name is an 'o', try to replace it to the right""" result = b'' for i in itertools.count(0): ch = get(y, x - i) if not _isname(ch): break result = ch + result for i in itertools.count(1): ch = get(y, x + i) if not _isname(ch): break result += ch if result == b'o': # special handling, find the name to the right result = b'' for i in itertools.count(2): ch = get(y, x + i) if ch == b' ' or ch in _pipechars: if result or x + i >= len(lines[y]): break else: result += ch return result or b'o' return result def parents(y, x): """(int, int) -> [str]. follow the ASCII edges at given position, return a list of parents""" visited = {(y, x)} visit = [] result = [] def follow(y, x, expected): """conditionally append (y, x) to visit array, if it's a char in excepted. 'o' in expected means an '_isname' test. if '-' (or '+') is not in excepted, and get(y, x) is '-' (or '+'), the next line (y + 1, x) will be checked instead.""" ch = get(y, x) if any(ch == c and c not in expected for c in (b'-', b'+')): y += 1 return follow(y + 1, x, expected) if ch in expected or (b'o' in expected and _isname(ch)): visit.append((y, x)) # -o- # starting point: # /|\ # follow '-' (horizontally), and '/|\' (to the bottom) follow(y + 1, x, b'|') follow(y + 1, x - 1, b'/') follow(y + 1, x + 1, b'\\') follow(y, x - 1, b'-') follow(y, x + 1, b'-') while visit: y, x = visit.pop() if (y, x) in visited: continue visited.add((y, x)) ch = get(y, x) if _isname(ch): result.append(getname(y, x)) continue elif ch == b'|': follow(y + 1, x, b'/|o') follow(y + 1, x - 1, b'/') follow(y + 1, x + 1, b'\\') elif ch == b'+': follow(y, x - 1, b'-') follow(y, x + 1, b'-') follow(y + 1, x - 1, b'/') follow(y + 1, x + 1, b'\\') follow(y + 1, x, b'|') elif ch == b'\\': follow(y + 1, x + 1, b'\\|o') elif ch == b'/': follow(y + 1, x - 1, b'/|o') elif ch == b'-': follow(y, x - 1, b'-+o') follow(y, x + 1, b'-+o') return result for y, line in enumerate(lines): for x, ch in enumerate(pycompat.bytestr(line)): if ch == b'#': # comment break if _isname(ch): edges[getname(y, x)] += parents(y, x) return dict(edges) class simplefilectx(object): def __init__(self, path, data): self._data = data self._path = path def data(self): return self._data def filenode(self): return None def path(self): return self._path def renamed(self): return None def flags(self): return b'' class simplecommitctx(context.committablectx): def __init__(self, repo, name, parentctxs, added): opts = { 'changes': scmutil.status([], list(added), [], [], [], [], []), 'date': b'0 0', 'extra': {b'branch': b'default'}, } super(simplecommitctx, self).__init__(repo, name, **opts) self._added = added self._parents = parentctxs while len(self._parents) < 2: self._parents.append(repo[node.nullid]) def filectx(self, key): return simplefilectx(key, self._added[key]) def commit(self): return self._repo.commitctx(self) def _walkgraph(edges): """yield node, parents in topologically order""" visible = set(edges.keys()) remaining = {} # {str: [str]} for k, vs in edges.items(): for v in vs: if v not in remaining: remaining[v] = [] remaining[k] = vs[:] while remaining: leafs = [k for k, v in remaining.items() if not v] if not leafs: raise error.Abort(_('the graph has cycles')) for leaf in sorted(leafs): if leaf in visible: yield leaf, edges[leaf] del remaining[leaf] for k, v in remaining.items(): if leaf in v: v.remove(leaf) def _getcomments(text): """ >>> [pycompat.sysstr(s) for s in _getcomments(br''' ... G ... | ... I D C F # split: B -> E, F, G ... \ \| | # replace: C -> D -> H ... H B E # prune: F, I ... \|/ ... A ... ''')] ['split: B -> E, F, G', 'replace: C -> D -> H', 'prune: F, I'] """ for line in text.splitlines(): if b' # ' not in line: continue yield line.split(b' # ', 1)[1].split(b' # ')[0].strip() @command(b'debugdrawdag', []) def debugdrawdag(ui, repo, **opts): """read an ASCII graph from stdin and create changesets The ASCII graph is like what :hg:`log -G` outputs, with each `o` replaced to the name of the node. The command will create dummy changesets and local tags with those names to make the dummy changesets easier to be referred to. If the name of a node is a single character 'o', It will be replaced by the word to the right. This makes it easier to reuse :hg:`log -G -T '{desc}'` outputs. For root (no parents) nodes, revset can be used to query existing repo. Note that the revset cannot have confusing characters which can be seen as the part of the graph edges, like `|/+-\`. """ text = ui.fin.read() # parse the graph and make sure len(parents) <= 2 for each node edges = _parseasciigraph(text) for k, v in edges.items(): if len(v) > 2: raise error.Abort(_('%s: too many parents: %s') % (k, b' '.join(v))) # parse comments to get extra file content instructions files = collections.defaultdict(dict) # {(name, path): content} comments = list(_getcomments(text)) filere = re.compile(br'^(\w+)/([\w/]+)\s*=\s*(.*)$', re.M) for name, path, content in filere.findall(b'\n'.join(comments)): content = content.replace(br'\n', b'\n').replace(br'\1', b'\1') files[name][path] = content committed = {None: node.nullid} # {name: node} # for leaf nodes, try to find existing nodes in repo for name, parents in edges.items(): if len(parents) == 0: try: committed[name] = scmutil.revsingle(repo, name) except error.RepoLookupError: pass # commit in topological order for name, parents in _walkgraph(edges): if name in committed: continue pctxs = [repo[committed[n]] for n in parents] pctxs.sort(key=lambda c: c.node()) added = {} if len(parents) > 1: # If it's a merge, take the files and contents from the parents for f in pctxs[1].manifest(): if f not in pctxs[0].manifest(): added[f] = pctxs[1][f].data() else: # If it's not a merge, add a single file added[name] = name # add extra file contents in comments for path, content in files.get(name, {}).items(): added[path] = content ctx = simplecommitctx(repo, name, pctxs, added) n = ctx.commit() committed[name] = n tagsmod.tag(repo, [name], n, message=None, user=None, date=None, local=True) # handle special comments with repo.wlock(), repo.lock(), repo.transaction(b'drawdag'): getctx = lambda x: repo.unfiltered()[committed[x.strip()]] for comment in comments: rels = [] # obsolete relationships args = comment.split(b':', 1) if len(args) <= 1: continue cmd = args[0].strip() arg = args[1].strip() if cmd in (b'replace', b'rebase', b'amend'): nodes = [getctx(m) for m in arg.split(b'->')] for i in range(len(nodes) - 1): rels.append((nodes[i], (nodes[i + 1],))) elif cmd in (b'split',): pre, succs = arg.split(b'->') succs = succs.split(b',') rels.append((getctx(pre), (getctx(s) for s in succs))) elif cmd in (b'prune',): for n in arg.split(b','): rels.append((getctx(n), ())) if rels: obsolete.createmarkers(repo, rels, date=(0, 0), operation=cmd)