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annotate mercurial/dirstateutils/docket.py @ 47682:78f7f0d490ee

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dirstate-v2: Move fixed-size tree metadata into the docket file Before this changeset, the dirstate-v2 data file contained not only nodes and paths that may be reused when appending to an existing file, but also some fixed-size metadata that applies to the entire tree and was added at the end of the data file for every append. This moves that metadata into the docket file, so that repeated "append" operations without meaningful changes don?t actually need to grow any file. Differential Revision: https://phab.mercurial-scm.org/D11098
author Simon Sapin <simon.sapin@octobus.net>
date Thu, 15 Jul 2021 23:02:17 +0200
parents ff97e793ed36
children 852262e2e7d9
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1 # dirstatedocket.py - docket file for dirstate-v2
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2 #
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3 # Copyright Mercurial Contributors
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4 #
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5 # This software may be used and distributed according to the terms of the
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6 # GNU General Public License version 2 or any later version.
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7
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8 from __future__ import absolute_import
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9
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10 import struct
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11
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12 from ..revlogutils import docket as docket_mod
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13
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14
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15 V2_FORMAT_MARKER = b"dirstate-v2\n"
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16
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17 # Must match the constant of the same name in
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18 # `rust/hg-core/src/dirstate_tree/on_disk.rs`
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19 TREE_METADATA_SIZE = 40
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20
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21 # * 12 bytes: format marker
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22 # * 32 bytes: node ID of the working directory's first parent
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23 # * 32 bytes: node ID of the working directory's second parent
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24 # * 4 bytes: big-endian used size of the data file
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25 # * {TREE_METADATA_SIZE} bytes: tree metadata, parsed separately
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26 # * 1 byte: length of the data file's UUID
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27 # * variable: data file's UUID
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28 #
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29 # Node IDs are null-padded if shorter than 32 bytes.
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30 # A data file shorter than the specified used size is corrupted (truncated)
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31 HEADER = struct.Struct(
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32 ">{}s32s32sL{}sB".format(len(V2_FORMAT_MARKER), TREE_METADATA_SIZE)
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33 )
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34
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35
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36 class DirstateDocket(object):
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37 data_filename_pattern = b'dirstate.%s.d'
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38
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39 def __init__(self, parents, data_size, tree_metadata, uuid):
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40 self.parents = parents
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41 self.data_size = data_size
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42 self.tree_metadata = tree_metadata
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43 self.uuid = uuid
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44
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45 @classmethod
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46 def with_new_uuid(cls, parents, data_size, tree_metadata):
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47 return cls(parents, data_size, tree_metadata, docket_mod.make_uid())
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48
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49 @classmethod
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50 def parse(cls, data, nodeconstants):
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51 if not data:
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52 parents = (nodeconstants.nullid, nodeconstants.nullid)
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53 return cls(parents, 0, b'', None)
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54 marker, p1, p2, data_size, meta, uuid_size = HEADER.unpack_from(data)
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55 if marker != V2_FORMAT_MARKER:
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56 raise ValueError("expected dirstate-v2 marker")
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57 uuid = data[HEADER.size : HEADER.size + uuid_size]
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58 p1 = p1[: nodeconstants.nodelen]
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59 p2 = p2[: nodeconstants.nodelen]
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60 return cls((p1, p2), data_size, meta, uuid)
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61
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62 def serialize(self):
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63 p1, p2 = self.parents
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64 header = HEADER.pack(
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65 V2_FORMAT_MARKER,
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66 p1,
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67 p2,
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68 self.data_size,
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69 self.tree_metadata,
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70 len(self.uuid),
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71 )
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72 return header + self.uuid
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73
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74 def data_filename(self):
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75 return self.data_filename_pattern % self.uuid