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annotate mercurial/revlogutils/docket.py @ 47245:616b8f412676

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revlogv2: introduce a very basic docket file This is the first stone toward using a docket file in revlogv2. Right now the docket is very basic and only store the version number (which is -also- stored into the index file?) and the other files have fixed name. This new implementation break transactionally? but they are no test checking transactionally for revlogv2? So I take this as an opportunity to start small. They are no usage of revlogv2 outside of tests anyway. The docket keeps the `.i` naming used by previous version index to preserve a unique entry point. We could decide to use a different name and look it up first, or to fully rework this in a future "store" version. However that does not seems necessary right now. We will re-introduces transactionality (and associated testing?) in a later changesets. A long list of TODOs have been added to the relevant comment. Differential Revision: https://phab.mercurial-scm.org/D10624
author Pierre-Yves David <pierre-yves.david@octobus.net>
date Mon, 03 May 2021 12:34:11 +0200
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children 6597255a4f94
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1 # docket - code related to revlog "docket"
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2 #
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3 # Copyright 2021 Pierre-Yves David <pierre-yves.david@octobus.net>
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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 ### Revlog docket file
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9 #
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10 # The revlog is stored on disk using multiple files:
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11 #
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12 # * a small docket file, containing metadata and a pointer,
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13 #
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14 # * an index file, containing fixed width information about revisions,
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15 #
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16 # * a data file, containing variable width data for these revisions,
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17
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18 from __future__ import absolute_import
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19
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20 import struct
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21
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22 from . import (
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23 constants,
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24 )
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25
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26 # Docket format
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27 #
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28 # * 4 bytes: revlog version
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29 # | This is mandatory as docket must be compatible with the previous
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30 # | revlog index header.
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31 S_HEADER = struct.Struct(constants.INDEX_HEADER.format)
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32
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33
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34 class RevlogDocket(object):
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35 """metadata associated with revlog"""
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36
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37 def __init__(self, revlog, version_header=None):
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38 self._version_header = version_header
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39 self._dirty = False
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40 self._radix = revlog.radix
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41 self._path = revlog._docket_file
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42 self._opener = revlog.opener
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43
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44 def index_filepath(self):
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45 """file path to the current index file associated to this docket"""
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46 # very simplistic version at first
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47 return b"%s.idx" % self._radix
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48
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49 def write(self, transaction):
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50 """write the modification of disk if any
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51
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52 This make the new content visible to all process"""
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53 if self._dirty:
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54 transaction.addbackup(self._path, location=b'store')
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55 with self._opener(self._path, mode=b'w', atomictemp=True) as f:
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56 f.write(self._serialize())
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57 self._dirty = False
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58
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59 def _serialize(self):
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60 return S_HEADER.pack(self._version_header)
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61
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62
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63 def default_docket(revlog, version_header):
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64 """given a revlog version a new docket object for the given revlog"""
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65 if (version_header & 0xFFFF) != constants.REVLOGV2:
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66 return None
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67 docket = RevlogDocket(revlog, version_header=version_header)
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68 docket._dirty = True
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69 return docket
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70
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71
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72 def parse_docket(revlog, data):
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73 """given some docket data return a docket object for the given revlog"""
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74 header = S_HEADER.unpack(data[: S_HEADER.size])
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75 (version_header,) = header
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76 docket = RevlogDocket(
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77 revlog,
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78 version_header=version_header,
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79 )
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80 return docket