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Differential D10791

revlog: move entry documentation alongside new related constants
ClosedPublic

Authored by marmoute on May 30 2021, 1:29 PM.

Details

Reviewers
indygreg
Alphare
Group Reviewers
hg-reviewers
Commits
rHG7a0ec25d5836: revlog: move entry documentation alongside new related constants
Summary

Accessing individual index-entry element is usually done using integer directly.
This is presumably for "performance reasons". However as the index entry gain
more and more element it seems useful to get the option to use symbolic constant
to access item, for both clarify and versatility. We will probably keep using
integer for performance critical path, but less critical code may start using
them now that they are declared.

Diff Detail

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Event Timeline

marmoute created this revision.May 30 2021, 1:29 PM
baymax updated this revision to Diff 28304.May 31 2021, 6:51 AM

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Alphare accepted this revision as: Alphare.May 31 2021, 10:36 AM
baymax updated this revision to Diff 28319.May 31 2021, 4:21 PM

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baymax updated this revision to Diff 28401.Jun 1 2021, 11:17 PM

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baymax updated this revision to Diff 28416.Jun 2 2021, 7:43 AM

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baymax updated this revision to Diff 28450.Jun 4 2021, 11:05 AM

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baymax updated this revision to Diff 28472.Jun 7 2021, 5:16 AM

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marmoute added a commit: rHG7a0ec25d5836: revlog: move entry documentation alongside new related constants.Jun 7 2021, 5:24 AM
This revision was not accepted when it landed; it landed in state Needs Review.
Closed by commit rHG7a0ec25d5836: revlog: move entry documentation alongside new related constants (authored by marmoute). · Explain Why
This revision was automatically updated to reflect the committed changes.

Revision Contents
Changeset List

PathPackages
Mmercurial/revlog.py (62 lines)
Mmercurial/revlogutils/constants.py (75 lines)

Diff 28494

mercurial/revlog.py

If `upperboundcomp` is not None, this is the expected maximal gain from If `upperboundcomp` is not None, this is the expected maximal gain from
compression for the data content. compression for the data content.
`concurrencychecker` is an optional function that receives 3 arguments: a `concurrencychecker` is an optional function that receives 3 arguments: a
file handle, a filename, and an expected position. It should check whether file handle, a filename, and an expected position. It should check whether
the current position in the file handle is valid, and log/warn/fail (by the current position in the file handle is valid, and log/warn/fail (by
raising). raising).
See mercurial/revlogutils/contants.py for details about the content of an
Internal details index entry.
----------------
A large part of the revlog logic deals with revisions' "index entries", tuple
objects that contains the same "items" whatever the revlog version.
Different versions will have different ways of storing these items (sometimes
not having them at all), but the tuple will always be the same. New fields
are usually added at the end to avoid breaking existing code that relies
on the existing order. The field are defined as follows:
[0] offset:
The byte index of the start of revision data chunk.
That value is shifted up by 16 bits. use "offset = field >> 16" to
retrieve it.
flags:
A flag field that carries special information or changes the behavior
of the revision. (see `REVIDX_*` constants for details)
The flag field only occupies the first 16 bits of this field,
use "flags = field & 0xFFFF" to retrieve the value.
[1] compressed length:
The size, in bytes, of the chunk on disk
[2] uncompressed length:
The size, in bytes, of the full revision once reconstructed.
[3] base rev:
Either the base of the revision delta chain (without general
delta), or the base of the delta (stored in the data chunk)
with general delta.
[4] link rev:
Changelog revision number of the changeset introducing this
revision.
[5] parent 1 rev:
Revision number of the first parent
[6] parent 2 rev:
Revision number of the second parent
[7] node id:
The node id of the current revision
[8] sidedata offset:
The byte index of the start of the revision's side-data chunk.
[9] sidedata chunk length:
The size, in bytes, of the revision's side-data chunk.
[10] data compression mode:
two bits that detail the way the data chunk is compressed on disk.
(see "COMP_MODE_*" constants for details). For revlog version 0 and
1 this will always be COMP_MODE_INLINE.
[11] side-data compression mode:
two bits that detail the way the sidedata chunk is compressed on disk.
(see "COMP_MODE_*" constants for details)
""" """
_flagserrorclass = error.RevlogError _flagserrorclass = error.RevlogError
def __init__( def __init__(
self, self,
opener, opener,
target, target,

mercurial/revlogutils/constants.py

ALL_KINDS = { ALL_KINDS = {
KIND_CHANGELOG, KIND_CHANGELOG,
KIND_MANIFESTLOG, KIND_MANIFESTLOG,
KIND_FILELOG, KIND_FILELOG,
KIND_OTHER, KIND_OTHER,
} }
### Index entry key
#
#
# Internal details
# ----------------
#
# A large part of the revlog logic deals with revisions' "index entries", tuple
# objects that contains the same "items" whatever the revlog version.
# Different versions will have different ways of storing these items (sometimes
# not having them at all), but the tuple will always be the same. New fields
# are usually added at the end to avoid breaking existing code that relies
# on the existing order. The field are defined as follows:
# [0] offset:
# The byte index of the start of revision data chunk.
# That value is shifted up by 16 bits. use "offset = field >> 16" to
# retrieve it.
#
# flags:
# A flag field that carries special information or changes the behavior
# of the revision. (see `REVIDX_*` constants for details)
# The flag field only occupies the first 16 bits of this field,
# use "flags = field & 0xFFFF" to retrieve the value.
ENTRY_DATA_OFFSET = 0
# [1] compressed length:
# The size, in bytes, of the chunk on disk
ENTRY_DATA_COMPRESSED_LENGTH = 1
# [2] uncompressed length:
# The size, in bytes, of the full revision once reconstructed.
ENTRY_DATA_UNCOMPRESSED_LENGTH = 2
# [3] base rev:
# Either the base of the revision delta chain (without general
# delta), or the base of the delta (stored in the data chunk)
# with general delta.
ENTRY_DELTA_BASE = 3
# [4] link rev:
# Changelog revision number of the changeset introducing this
# revision.
ENTRY_LINK_REV = 4
# [5] parent 1 rev:
# Revision number of the first parent
ENTRY_PARENT_1 = 5
# [6] parent 2 rev:
# Revision number of the second parent
ENTRY_PARENT_2 = 6
# [7] node id:
# The node id of the current revision
ENTRY_NODE_ID = 7
# [8] sidedata offset:
# The byte index of the start of the revision's side-data chunk.
ENTRY_SIDEDATA_OFFSET = 8
# [9] sidedata chunk length:
# The size, in bytes, of the revision's side-data chunk.
ENTRY_SIDEDATA_COMPRESSED_LENGTH = 9
# [10] data compression mode:
# two bits that detail the way the data chunk is compressed on disk.
# (see "COMP_MODE_*" constants for details). For revlog version 0 and
# 1 this will always be COMP_MODE_INLINE.
ENTRY_DATA_COMPRESSION_MODE = 10
# [11] side-data compression mode:
# two bits that detail the way the sidedata chunk is compressed on disk.
# (see "COMP_MODE_*" constants for details)
ENTRY_SIDEDATA_COMPRESSION_MODE = 11
### main revlog header ### main revlog header
# We cannot rely on Struct.format is inconsistent for python <=3.6 versus above # We cannot rely on Struct.format is inconsistent for python <=3.6 versus above
INDEX_HEADER_FMT = b">I" INDEX_HEADER_FMT = b">I"
INDEX_HEADER = struct.Struct(INDEX_HEADER_FMT) INDEX_HEADER = struct.Struct(INDEX_HEADER_FMT)
## revlog version ## revlog version
REVLOGV0 = 0 REVLOGV0 = 0