Cache restore sometimes downloads ~0MB caches

We use the cache for tools installed with asdf, and for perl libraries. We have a flaky bug where sometimes, the same cache that works fine on a branch doesn’t work on another branch, and a ~0MB archive is downloaded. This has been happening randomly over the last 6 months (maybe once every 30/40 pull request).

Example:

On both branches A and B, our install-dev-tools job sees that we haven’t updated anything, and gets a cache hit:

Post job cleanup.
Post job cleanup.
Cache hit occurred on the primary key Linux-yarn-cache-07a3008bf228aaf955d98ce084eb8e6b09b623263d80578af5b7d65840fbbbe3-v2, not saving cache.
Post job cleanup.
Cache hit occurred on the primary key Linux-perl-cache-391933be47fcbd2760fbcccebd7446cf5f0f10d80e572e5adeeb9c4f9f62b6e8-v2, not saving cache.
Post job cleanup.
Cache hit occurred on the primary key Linux-asdf-cache-8093192a4cdff5685410dbe3b09b322ef56cc2496b4af9cf83ac7196aafffb7c, not saving cache.

On branch A, the subsequent job, running tests, restores the cache and everything works well:

Run actions/cache@v2
  with:
    path: ~/.asdf
  
    key: Linux-asdf-cache-8093192a4cdff5685410dbe3b09b322ef56cc2496b4af9cf83ac7196aafffb7c
  env:
    PGUSER: postgres
    ASDF_DIR: /home/runner/.asdf
    ASDF_DATA_DIR: /home/runner/.asdf
    PERL5LIB: /home/runner/perl5/lib/perl5
    PERL_LOCAL_LIB_ROOT: /home/runner/perl5
    PERL_MB_OPT: --install_base '/home/runner/perl5'
    PERL_MM_OPT: INSTALL_BASE=/home/runner/perl5
Received 176160768 of 261546746 (67.4%), 167.8 MBs/sec
Received 261546746 of 261546746 (100.0%), 158.1 MBs/sec
Cache Size: ~249 MB (261546746 B)
/usr/bin/tar --use-compress-program zstd -d -xf /home/runner/work/_temp/301a4ee1-882b-4c9d-8005-1ffe324dadbb/cache.tzst -P -C /home/runner/work/cas-cif/cas-cif
Cache restored successfully

Cache restored from key: Linux-asdf-cache-8093192a4cdff5685410dbe3b09b322ef56cc2496b4af9cf83ac7196aafffb7c

Now, on branch B, for some reason, the cache is different, and the job fails later, because it is missing the executable the cache was supposed to restore. Note the difference in cache size

Run actions/cache@v2
  with:
    path: ~/.asdf
  
    key: Linux-asdf-cache-8093192a4cdff5685410dbe3b09b322ef56cc2496b4af9cf83ac7196aafffb7c
  env:
    PGUSER: postgres
    ASDF_DIR: /home/runner/.asdf
    ASDF_DATA_DIR: /home/runner/.asdf
    PERL5LIB: /home/runner/perl5/lib/perl5
    PERL_LOCAL_LIB_ROOT: /home/runner/perl5
    PERL_MB_OPT: --install_base '/home/runner/perl5'
    PERL_MM_OPT: INSTALL_BASE=/home/runner/perl5
Received 413443 of 413443 (100.0%), 5.8 MBs/sec
Cache Size: ~0 MB (413443 B)
/usr/bin/tar --use-compress-program zstd -d -xf /home/runner/work/_temp/77537a38-6e05-4b3b-9f00-eecc3d3b5904/cache.tzst -P -C /home/runner/work/cas-cif/cas-cif
Cache restored successfully

Cache restored from key: Linux-asdf-cache-8093192a4cdff5685410dbe3b09b322ef56cc2496b4af9cf83ac7196aafffb7c

[matthieu-foucault]

Nevermind, the issue my latest message above is expected behaviour due to misconfiguration of our workflow. Closing this issue, I’ll open a new one if I see this happening again with a properly configured workflow

[matthieu-foucault]

Hi @kotewar , just encountered it now in https://github.com/bcgov/CONN-CCBC-portal/runs/8073512335?check_suite_focus=true:

Run actions/cache@v2
  with:
    path: ~/.asdf
  
    key: Linux-asdf-cache-fcc9bf91c47d06add757287d0fb86747258f3ba45ca5cc3de4a6a744ee1a6410
  env:
    PGPASSWORD: postgres
    PGUSER: postgres
    PGDATABASE: ccbc
    ASDF_DIR: /home/runner/.asdf
    ASDF_DATA_DIR: /home/runner/.asdf
    PERL5LIB: /home/runner/perl5/lib/perl5
    PERL_LOCAL_LIB_ROOT: /home/runner/perl5
    PERL_MB_OPT: --install_base '/home/runner/perl5'
    PERL_MM_OPT: INSTALL_BASE=/home/runner/perl5
Received 394868 of 394868 (100.0%), 1.4 MBs/sec
Cache Size: ~0 MB (394868 B)
/usr/bin/tar --use-compress-program zstd -d -xf /home/runner/work/_temp/d6403261-63cd-4882-9d71-178db5f5faa7/cache.tzst -P -C /home/runner/work/CONN-CCBC-portal/CONN-CCBC-portal
Cache restored successfully