indygreg created this revision. Herald added a subscriber: mercurial-devel. Herald added a reviewer: hg-reviewers.
REVISION SUMMARY Revlog behavior should live as close to the revlog as possible. In version 1 revlogs, we engaged sparse semantics by using a repository requirement. This constituted action at a distance and wasn't optimal. This commit introduces a feature flag on version 2 revlogs that explicitly denotes whether sparse reading semantics are enabled. The flag is enabled by default for version 2 revlogs. In order to get the flag enabled by default, we had to tweak localrepo's logic for populating opener options to only set "sparse-revlog" if the requirement was present. This lets the revlog initializer use sane defaults depending on the revlog version. (The interaction between opener options and the revlog class is kinda wonky and could use a re-think. But my little brain isn't prepared to handle that at this time.) I'm also a bit unsure why we have 2 attributes controlling sparse behavior (revlog._sparserevlog and revlog._withsparseread). I *think* they can be consolidated. But I'm not sure. The new revlog feature flag implies both, which seems reasonable. REPOSITORY rHG Mercurial REVISION DETAIL https://phab.mercurial-scm.org/D5565 AFFECTED FILES mercurial/help/internals/revlogs.txt mercurial/localrepo.py mercurial/revlog.py mercurial/revlogutils/constants.py tests/test-revlog-v2.t CHANGE DETAILS diff --git a/tests/test-revlog-v2.t b/tests/test-revlog-v2.t --- a/tests/test-revlog-v2.t +++ b/tests/test-revlog-v2.t @@ -22,7 +22,7 @@ $ cd empty-repo $ cat .hg/requires dotencode - exp-revlogv2.1 + exp-revlogv2.2 fncache sparserevlog store @@ -58,8 +58,8 @@ $ f --hexdump --bytes 4 .hg/store/00changelog.i .hg/store/00changelog.i: - 0000: 00 01 de ad |....| + 0000: 00 03 de ad |....| $ f --hexdump --bytes 4 .hg/store/data/foo.i .hg/store/data/foo.i: - 0000: 00 01 de ad |....| + 0000: 00 03 de ad |....| diff --git a/mercurial/revlogutils/constants.py b/mercurial/revlogutils/constants.py --- a/mercurial/revlogutils/constants.py +++ b/mercurial/revlogutils/constants.py @@ -24,11 +24,13 @@ FLAG_INLINE_DATA = (1 << 16) # Only used by v1, implied by v2. FLAG_GENERALDELTA = (1 << 17) +# Only used by v2. +FLAG_SPARSE_DELTA_CHAINS = (1 << 17) REVLOG_DEFAULT_FLAGS = FLAG_INLINE_DATA REVLOG_DEFAULT_FORMAT = REVLOGV1 REVLOG_DEFAULT_VERSION = REVLOG_DEFAULT_FORMAT | REVLOG_DEFAULT_FLAGS REVLOGV1_FLAGS = FLAG_INLINE_DATA | FLAG_GENERALDELTA -REVLOGV2_FLAGS = FLAG_INLINE_DATA +REVLOGV2_FLAGS = FLAG_INLINE_DATA | FLAG_SPARSE_DELTA_CHAINS # revlog index flags diff --git a/mercurial/revlog.py b/mercurial/revlog.py --- a/mercurial/revlog.py +++ b/mercurial/revlog.py @@ -37,6 +37,7 @@ from .revlogutils.constants import ( FLAG_GENERALDELTA, FLAG_INLINE_DATA, + FLAG_SPARSE_DELTA_CHAINS, REVIDX_DEFAULT_FLAGS, REVIDX_ELLIPSIS, REVIDX_EXTSTORED, @@ -83,6 +84,7 @@ REVLOGV2 FLAG_INLINE_DATA FLAG_GENERALDELTA +FLAG_SPARSE_DELTA_CHAINS REVLOG_DEFAULT_FLAGS REVLOG_DEFAULT_FORMAT REVLOG_DEFAULT_VERSION @@ -392,6 +394,10 @@ if 'revlogv2' in opts: newversionflags = REVLOGV2 | FLAG_INLINE_DATA + + if 'sparse-revlog' not in opts or opts.get('sparse-revlog'): + newversionflags |= FLAG_SPARSE_DELTA_CHAINS + elif 'revlogv1' in opts: newversionflags = REVLOGV1 | FLAG_INLINE_DATA if 'generaldelta' in opts: @@ -412,10 +418,6 @@ self._maxdeltachainspan = opts['maxdeltachainspan'] if self._mmaplargeindex and 'mmapindexthreshold' in opts: mmapindexthreshold = opts['mmapindexthreshold'] - self._sparserevlog = bool(opts.get('sparse-revlog', False)) - withsparseread = bool(opts.get('with-sparse-read', False)) - # sparse-revlog forces sparse-read - self._withsparseread = self._sparserevlog or withsparseread if 'sparse-read-density-threshold' in opts: self._srdensitythreshold = opts['sparse-read-density-threshold'] if 'sparse-read-min-gap-size' in opts: @@ -467,6 +469,8 @@ self._inline = False self._generaldelta = False + self._sparserevlog = False + self._withsparseread = False elif fmt == REVLOGV1: if flags & ~REVLOGV1_FLAGS: @@ -477,6 +481,11 @@ self._inline = versionflags & FLAG_INLINE_DATA self._generaldelta = versionflags & FLAG_GENERALDELTA + self._sparserevlog = bool(opts.get('sparse-revlog', False)) + withsparseread = bool(opts.get('with-sparse-read', False)) + # sparse-revlog forces sparse-read + self._withsparseread = self._sparserevlog or withsparseread + elif fmt == REVLOGV2: if flags & ~REVLOGV2_FLAGS: raise error.RevlogError(_('unknown flags (%#04x) in version %d ' @@ -487,6 +496,9 @@ # generaldelta implied by version 2 revlogs. self._generaldelta = True + self._sparserevlog = versionflags & FLAG_SPARSE_DELTA_CHAINS + self._withsparseread = versionflags & FLAG_SPARSE_DELTA_CHAINS + else: raise error.RevlogError(_('unknown version (%d) in revlog %s') % (fmt, self.indexfile)) diff --git a/mercurial/localrepo.py b/mercurial/localrepo.py --- a/mercurial/localrepo.py +++ b/mercurial/localrepo.py @@ -363,7 +363,7 @@ # Increment the sub-version when the revlog v2 format changes to lock out old # clients. -REVLOGV2_REQUIREMENT = 'exp-revlogv2.1' +REVLOGV2_REQUIREMENT = 'exp-revlogv2.2' # A repository with the sparserevlog feature will have delta chains that # can spread over a larger span. Sparse reading cuts these large spans into @@ -772,8 +772,8 @@ options[b'sparse-read-min-gap-size'] = srmingapsize sparserevlog = SPARSEREVLOG_REQUIREMENT in requirements - options[b'sparse-revlog'] = sparserevlog if sparserevlog: + options[b'sparse-revlog'] = True options[b'generaldelta'] = True maxchainlen = None diff --git a/mercurial/help/internals/revlogs.txt b/mercurial/help/internals/revlogs.txt --- a/mercurial/help/internals/revlogs.txt +++ b/mercurial/help/internals/revlogs.txt @@ -66,6 +66,13 @@ 0 Store revision data inline. +1 + Sparse delta chains. When set, delta chains (see below) may cover + long spans in the revlog and readers should perform sparse reads to + minimize the number of bytes that must be read to resolve a revision. + Historically, revlogs limited the total linear span between a revision's + first and last delta and readers performed a read of all the bytes + in between. The following header values are common: @@ -162,6 +169,9 @@ There is no dedicated *generaldelta* revlog format flag. Instead, the feature is implied enabled by default. +There is a revlog format flag that indicates whether sparse delta chains +and reading should be used. + Delta Chains ============ To: indygreg, #hg-reviewers Cc: mercurial-devel _______________________________________________ Mercurial-devel mailing list Mercurial-devel@mercurial-scm.org https://www.mercurial-scm.org/mailman/listinfo/mercurial-devel