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Cache non-symlinks in realpathSync #10253

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Cache non-symlinks in realpathSync #10253

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yallop
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@yallop yallop commented Dec 13, 2016

Background

The fs.realpathSync function synchronously traverses paths componentwise to resolve symbolic links.

The optional cache argument stores the results of resolution to avoid repeated lookups. The cache can be used to override resolution and to store the results of calls to readlinkSync.

However, the cache only records paths that lstat reveals to be symlinks. Consequently, a call to fs.realpathSync for a path without symlinks may result in many calls to lstat, even if most parts of the path have been resolved in an earlier call.

Checklist
  • make -j4 test (UNIX), or vcbuild test nosign (Windows) passes
  • commit message follows commit guidelines
Affected core subsystem(s)

fs

Description of change

This tiny patch extends fs.realpathSync to record the results for paths that are not symlinks. The code suggests that this was originally the intention, since the cache is expected to contain entries that resolve to themselves:

cache.get(base) === base

With this patch a run of ember build on a fresh application makes around 6,200 fewer lstat calls (out of a total of around 70,000 syscalls). On a typical native file system the performance difference is negligible, but in situations where a syscall has more significant overhead it can be a worthwhile saving. For example, with a file system that forwards operations over a socket via FUSE this patch saves around 10% of the build time.

@yallop
Cache non-symlinks in realpathSync.
d3276fd 
Extend `fs.realpathSync` to cache the results for paths that are not
symlinks in addition to caching symlink mappings.

Signed-off-by: Jeremy Yallop <[email protected]>
@nodejs-github-bot nodejs-github-bot added fs Issues and PRs related to the fs subsystem / file system. lts-watch-v6.x labels Dec 13, 2016
@mscdex
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mscdex commented Dec 13, 2016

What about fs.realPath()?

@addaleax
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What about fs.realpath()?

We removed the cache argument in v6. The cache in fs.realpathSync is exlusively used by the module loader now, not part of a public API.

addaleax
addaleax approved these changes Dec 13, 2016
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LGTM with green CI

CI: https://ci.nodejs.org/job/node-test-commit/6630/
CITGM: https://ci.nodejs.org/view/Node.js-citgm/job/citgm-smoker/479/

@addaleax addaleax added the performance Issues and PRs related to the performance of Node.js. label Dec 13, 2016
@yallop
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yallop commented Dec 14, 2016

Thanks for the reviews. I'm not sure why the test/arm CI failed, but let me know if there's anything more I need to do here.

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gibfahn commented Dec 23, 2016 •
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CI 2: https://ci.nodejs.org/job/node-test-commit/6831/
CITGM 2: https://ci.nodejs.org/view/Node.js-citgm/job/citgm-smoker/497/

(ARM failures were probably machine issues)

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Trott commented Dec 23, 2016

OS X failure looks like an unrelated race condition in test-http-client-timeout-with-data to me but let's re-run CI to confirm...

CI: https://ci.nodejs.org/job/node-test-pull-request/5561/

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Trott commented Dec 23, 2016

Hmmm, now an AIX failure, also seemingly unrelated. Peculiar.

Let's try again:

CI: https://ci.nodejs.org/job/node-test-pull-request/5562/

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Trott commented Dec 23, 2016

There we go. CI is ✅

jasnell pushed a commit that referenced this pull request Dec 24, 2016
@yallop @jasnell
fs: cache non-symlinks in realpathSync.
5dc4487 
Extend `fs.realpathSync` to cache the results for paths that are not
symlinks in addition to caching symlink mappings.

PR-URL: #10253
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: James M Snell <[email protected]>
@jasnell
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jasnell commented Dec 24, 2016

Landed in 5dc4487

@jasnell jasnell closed this Dec 24, 2016
@yallop yallop deleted the cache-non-symlinks branch December 26, 2016 10:35
@evanlucas evanlucas mentioned this pull request Jan 3, 2017
Merged
evanlucas pushed a commit that referenced this pull request Jan 3, 2017
@yallop @evanlucas
fs: cache non-symlinks in realpathSync.
094a960 
Extend `fs.realpathSync` to cache the results for paths that are not
symlinks in addition to caching symlink mappings.

PR-URL: #10253
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: James M Snell <[email protected]>
evanlucas pushed a commit that referenced this pull request Jan 4, 2017
@yallop @evanlucas
fs: cache non-symlinks in realpathSync.
6629f8f 
Extend `fs.realpathSync` to cache the results for paths that are not
symlinks in addition to caching symlink mappings.

PR-URL: #10253
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: James M Snell <[email protected]>
@MylesBorins
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I've gone ahead and backported to v6.x, but am a little bit wary. Is this a good change to backport? It did not land cleanly on v4.x, which makes sense to me. As such I added the appropriate don't land label

MylesBorins pushed a commit that referenced this pull request Jan 23, 2017
@yallop @MylesBorins
fs: cache non-symlinks in realpathSync.
abc7106 
Extend `fs.realpathSync` to cache the results for paths that are not
symlinks in addition to caching symlink mappings.

PR-URL: #10253
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: James M Snell <[email protected]>
MylesBorins pushed a commit that referenced this pull request Jan 24, 2017
@yallop @MylesBorins
fs: cache non-symlinks in realpathSync.
f9ff4ec 
Extend `fs.realpathSync` to cache the results for paths that are not
symlinks in addition to caching symlink mappings.

PR-URL: #10253
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: James M Snell <[email protected]>
@MylesBorins MylesBorins mentioned this pull request Jan 24, 2017
Merged
MylesBorins pushed a commit that referenced this pull request Jan 31, 2017
@yallop @MylesBorins
fs: cache non-symlinks in realpathSync.
709b9b4 
Extend `fs.realpathSync` to cache the results for paths that are not
symlinks in addition to caching symlink mappings.

PR-URL: #10253
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: James M Snell <[email protected]>
MylesBorins added a commit that referenced this pull request Feb 21, 2017
@MylesBorins
2017-02-21, Version 6.10.0 'Boron' (LTS)
1b6fd44 
Notable Changes:

The SEMVER-MINOR changes include:

*  crypto: allow adding extra certs to well-known CAs (Sam Roberts)
   #9139
*  deps: Upgrade INTL ICU to version 58 (Steven R. Loomis)
   #9234
*  process: add `process.memoryUsage.external` (Fedor Indutny)
   #9587
*  src: add wrapper for process.emitWarning() (Sam Roberts)
   #9139

Notable SEMVER-PATCH changes include:

*  fs: cache non-symlinks in realpathSync. (Jeremy Yallop)
   #10253
*  repl: allow autocompletion for scoped packages (Evan Lucas)
   #10296
MylesBorins added a commit that referenced this pull request Feb 22, 2017
@MylesBorins
2017-02-21, Version 6.10.0 'Boron' (LTS)
aecb085 
Notable Changes:

The SEMVER-MINOR changes include:

*  crypto: allow adding extra certs to well-known CAs (Sam Roberts)
   #9139
*  deps: Upgrade INTL ICU to version 58 (Steven R. Loomis)
   #9234
*  process: add `process.memoryUsage.external` (Fedor Indutny)
   #9587
*  src: add wrapper for process.emitWarning() (Sam Roberts)
   #9139

Notable SEMVER-PATCH changes include:

*  fs: cache non-symlinks in realpathSync. (Jeremy Yallop)
   #10253
*  repl: allow autocompletion for scoped packages (Evan Lucas)
   #10296

PR-URL: #10974
imyller added a commit to imyller/meta-nodejs that referenced this pull request Mar 2, 2017
@imyller
2017-02-21, Version 6.10.0 'Boron' (LTS)
edbc1bf 
    Notable Changes:

    The SEMVER-MINOR changes include:

    *  crypto: allow adding extra certs to well-known CAs (Sam Roberts)
       nodejs/node#9139
    *  deps: Upgrade INTL ICU to version 58 (Steven R. Loomis)
       nodejs/node#9234
    *  process: add `process.memoryUsage.external` (Fedor Indutny)
       nodejs/node#9587
    *  src: add wrapper for process.emitWarning() (Sam Roberts)
       nodejs/node#9139

    Notable SEMVER-PATCH changes include:

    *  fs: cache non-symlinks in realpathSync. (Jeremy Yallop)
       nodejs/node#10253
    *  repl: allow autocompletion for scoped packages (Evan Lucas)
       nodejs/node#10296

Signed-off-by: Ilkka Myller <[email protected]>
imyller added a commit to imyller/meta-nodejs that referenced this pull request Mar 2, 2017
@imyller
2017-02-21, Version 6.10.0 'Boron' (LTS)
f99e583 
    Notable Changes:

    The SEMVER-MINOR changes include:

    *  crypto: allow adding extra certs to well-known CAs (Sam Roberts)
       nodejs/node#9139
    *  deps: Upgrade INTL ICU to version 58 (Steven R. Loomis)
       nodejs/node#9234
    *  process: add `process.memoryUsage.external` (Fedor Indutny)
       nodejs/node#9587
    *  src: add wrapper for process.emitWarning() (Sam Roberts)
       nodejs/node#9139

    Notable SEMVER-PATCH changes include:

    *  fs: cache non-symlinks in realpathSync. (Jeremy Yallop)
       nodejs/node#10253
    *  repl: allow autocompletion for scoped packages (Evan Lucas)
       nodejs/node#10296

Signed-off-by: Ilkka Myller <[email protected]>
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@addaleax addaleax addaleax approved these changes

@jasnell jasnell jasnell approved these changes

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@yallop @mscdex @addaleax @gibfahn @Trott @jasnell @MylesBorins @nodejs-github-bot