view tests/test-contrib-perf.t @ 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

#require test-repo

Set vars:

  $ . "$TESTDIR/helpers-testrepo.sh"
  $ CONTRIBDIR="$TESTDIR/../contrib"

Prepare repo:

  $ hg init

  $ echo this is file a > a
  $ hg add a
  $ hg commit -m first

  $ echo adding to file a >> a
  $ hg commit -m second

  $ echo adding more to file a >> a
  $ hg commit -m third

  $ hg up -r 0
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo merge-this >> a
  $ hg commit -m merge-able
  created new head

  $ hg up -r 2
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

perfstatus

  $ cat >> $HGRCPATH << EOF
  > [extensions]
  > perfstatusext=$CONTRIBDIR/perf.py
  > [perf]
  > presleep=0
  > stub=on
  > parentscount=1
  > EOF
  $ hg help perfstatusext
  perfstatusext extension - helper extension to measure performance
  
  list of commands:
  
   perfaddremove
                 (no help text available)
   perfancestors
                 (no help text available)
   perfancestorset
                 (no help text available)
   perfannotate  (no help text available)
   perfbdiff     benchmark a bdiff between revisions
   perfbookmarks
                 benchmark parsing bookmarks from disk to memory
   perfbranchmap
                 benchmark the update of a branchmap
   perfbranchmapload
                 benchmark reading the branchmap
   perfbundleread
                 Benchmark reading of bundle files.
   perfcca       (no help text available)
   perfchangegroupchangelog
                 Benchmark producing a changelog group for a changegroup.
   perfchangeset
                 (no help text available)
   perfctxfiles  (no help text available)
   perfdiffwd    Profile diff of working directory changes
   perfdirfoldmap
                 (no help text available)
   perfdirs      (no help text available)
   perfdirstate  (no help text available)
   perfdirstatedirs
                 (no help text available)
   perfdirstatefoldmap
                 (no help text available)
   perfdirstatewrite
                 (no help text available)
   perffncacheencode
                 (no help text available)
   perffncacheload
                 (no help text available)
   perffncachewrite
                 (no help text available)
   perfheads     (no help text available)
   perfindex     (no help text available)
   perflinelogedits
                 (no help text available)
   perfloadmarkers
                 benchmark the time to parse the on-disk markers for a repo
   perflog       (no help text available)
   perflookup    (no help text available)
   perflrucachedict
                 (no help text available)
   perfmanifest  benchmark the time to read a manifest from disk and return a
                 usable
   perfmergecalculate
                 (no help text available)
   perfmoonwalk  benchmark walking the changelog backwards
   perfnodelookup
                 (no help text available)
   perfparents   (no help text available)
   perfpathcopies
                 (no help text available)
   perfphases    benchmark phasesets computation
   perfphasesremote
                 benchmark time needed to analyse phases of the remote server
   perfrawfiles  (no help text available)
   perfrevlogchunks
                 Benchmark operations on revlog chunks.
   perfrevlogindex
                 Benchmark operations against a revlog index.
   perfrevlogrevision
                 Benchmark obtaining a revlog revision.
   perfrevlogrevisions
                 Benchmark reading a series of revisions from a revlog.
   perfrevrange  (no help text available)
   perfrevset    benchmark the execution time of a revset
   perfstartup   (no help text available)
   perfstatus    (no help text available)
   perftags      (no help text available)
   perftemplating
                 test the rendering time of a given template
   perfunidiff   benchmark a unified diff between revisions
   perfvolatilesets
                 benchmark the computation of various volatile set
   perfwalk      (no help text available)
   perfwrite     microbenchmark ui.write
  
  (use 'hg help -v perfstatusext' to show built-in aliases and global options)
  $ hg perfaddremove
  $ hg perfancestors
  $ hg perfancestorset 2
  $ hg perfannotate a
  $ hg perfbdiff -c 1
  $ hg perfbdiff --alldata 1
  $ hg perfunidiff -c 1
  $ hg perfunidiff --alldata 1
  $ hg perfbookmarks
  $ hg perfbranchmap
  $ hg perfcca
  $ hg perfchangegroupchangelog
  $ hg perfchangeset 2
  $ hg perfctxfiles 2
  $ hg perfdiffwd
  $ hg perfdirfoldmap
  $ hg perfdirs
  $ hg perfdirstate
  $ hg perfdirstatedirs
  $ hg perfdirstatefoldmap
  $ hg perfdirstatewrite
#if repofncache
  $ hg perffncacheencode
  $ hg perffncacheload
  $ hg debugrebuildfncache
  fncache already up to date
  $ hg perffncachewrite
  $ hg debugrebuildfncache
  fncache already up to date
#endif
  $ hg perfheads
  $ hg perfindex
  $ hg perflinelogedits -n 1
  $ hg perfloadmarkers
  $ hg perflog
  $ hg perflookup 2
  $ hg perflrucache
  $ hg perfmanifest 2
  $ hg perfmanifest -m 44fe2c8352bb3a478ffd7d8350bbc721920134d1
  $ hg perfmanifest -m 44fe2c8352bb
  abort: manifest revision must be integer or full node
  [255]
  $ hg perfmergecalculate -r 3
  $ hg perfmoonwalk
  $ hg perfnodelookup 2
  $ hg perfpathcopies 1 2
  $ hg perfrawfiles 2
  $ hg perfrevlogindex -c
#if reporevlogstore
  $ hg perfrevlogrevisions .hg/store/data/a.i
#endif
  $ hg perfrevlogrevision -m 0
  $ hg perfrevlogchunks -c
  $ hg perfrevrange
  $ hg perfrevset 'all()'
  $ hg perfstartup
  $ hg perfstatus
  $ hg perftags
  $ hg perftemplating
  $ hg perfvolatilesets
  $ hg perfwalk
  $ hg perfparents

test actual output
------------------

normal output:

  $ hg perfheads --config perf.stub=no
  ! wall * comb * user * sys * (best of *) (glob)

detailed output:

  $ hg perfheads --config perf.all-timing=yes --config perf.stub=no
  ! wall * comb * user * sys * (best of *) (glob)
  ! wall * comb * user * sys * (max of *) (glob)
  ! wall * comb * user * sys * (avg of *) (glob)
  ! wall * comb * user * sys * (median of *) (glob)

test json output
----------------

normal output:

  $ hg perfheads --template json --config perf.stub=no
  [
   {
    "comb": *, (glob)
    "count": *, (glob)
    "sys": *, (glob)
    "user": *, (glob)
    "wall": * (glob)
   }
  ]

detailed output:

  $ hg perfheads --template json --config perf.all-timing=yes --config perf.stub=no
  [
   {
    "avg.comb": *, (glob)
    "avg.count": *, (glob)
    "avg.sys": *, (glob)
    "avg.user": *, (glob)
    "avg.wall": *, (glob)
    "comb": *, (glob)
    "count": *, (glob)
    "max.comb": *, (glob)
    "max.count": *, (glob)
    "max.sys": *, (glob)
    "max.user": *, (glob)
    "max.wall": *, (glob)
    "median.comb": *, (glob)
    "median.count": *, (glob)
    "median.sys": *, (glob)
    "median.user": *, (glob)
    "median.wall": *, (glob)
    "sys": *, (glob)
    "user": *, (glob)
    "wall": * (glob)
   }
  ]

Check perf.py for historical portability
----------------------------------------

  $ cd "$TESTDIR/.."

  $ (testrepohg files -r 1.2 glob:mercurial/*.c glob:mercurial/*.py;
  >  testrepohg files -r tip glob:mercurial/*.c glob:mercurial/*.py) |
  > "$TESTDIR"/check-perf-code.py contrib/perf.py
  contrib/perf.py:\d+: (re)
   >     from mercurial import (
   import newer module separately in try clause for early Mercurial
  contrib/perf.py:\d+: (re)
   >     from mercurial import (
   import newer module separately in try clause for early Mercurial
  [1]