One thing that we haven't discussed (afaik) is how to treat metrics that shouldn't expire -- or do we believe that all metrics should expire?  Along the same lines, we should probably establish a guideline for the default expected lifetime for a metric.

(Not intending to derail forward progress on this work!  We can work out the above in parallel with implementing the basics.)

Yeah, I don't think we've fully settled on requiring an expiry date. I'm tempted to say that we should move towards that world though. I wouldn't mind seeing regular re-evaluation of our core metrics to make sure they're still valid. I am also worried about having a bunch of "bump the expiry" CLs to review though! It would also be fairly annoying for metrics owners to have to frequently create these CLs.

We've had some discussions about easing both sides of overhead. We were considering building a system that would let owners click a button to bump the expiry, and possibly also an automated review system for such changes. Very early thinking in that area though.

I also agree that we need to establish a guideline for expected lifetimes.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e5e54f0167c142e1af0d097fd5396283edac2d45

commit e5e54f0167c142e1af0d097fd5396283edac2d45
Author: Ira Burak <iburak@google.com>
Date: Tue Jul 18 20:03:19 2017

Added handling of expiry dates to validating.
Bug:744672

Change-Id: Iccb9cfade3b5e39e489adbeb0c2b6a2509240afc
Reviewed-on: https://chromium-review.googlesource.com/576063
Commit-Queue: Ira Burak <iburak@google.com>
Reviewed-by: Jesse Doherty <jwd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487570}
[modify] https://crrev.com/e5e54f0167c142e1af0d097fd5396283edac2d45/tools/metrics/histograms/extract_histograms.py
[modify] https://crrev.com/e5e54f0167c142e1af0d097fd5396283edac2d45/tools/metrics/histograms/print_style.py

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/ffeffa2e7e0d2e293bee4b080c432c181cef0ff9

commit ffeffa2e7e0d2e293bee4b080c432c181cef0ff9
Author: Ira Burak <iburak@google.com>
Date: Fri Jul 21 15:54:18 2017

Fix a typo error.
Store expiry date as string.

Bug:  744672 
Change-Id: I83f9548ebe6a3a1e004d48476a5eed020d37b817
Reviewed-on: https://chromium-review.googlesource.com/578438
Commit-Queue: Ira Burak <iburak@google.com>
Reviewed-by: Jesse Doherty <jwd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#488668}
[modify] https://crrev.com/ffeffa2e7e0d2e293bee4b080c432c181cef0ff9/tools/metrics/histograms/extract_histograms.py

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4ad351a3ff5d2475943eb7a03cddfc2a10fdb2fb

commit 4ad351a3ff5d2475943eb7a03cddfc2a10fdb2fb
Author: Ira Burak <iburak@google.com>
Date: Sat Jul 29 00:19:53 2017

Changing extract_histograms.py to store expiry dates as strings instead of objects.

Bug:  744672 
Change-Id: I36d755a84035388e22cf30de06fa8c8555f410cc
Reviewed-on: https://chromium-review.googlesource.com/584850
Commit-Queue: Ira Burak <iburak@google.com>
Reviewed-by: Jesse Doherty <jwd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#490552}
[modify] https://crrev.com/4ad351a3ff5d2475943eb7a03cddfc2a10fdb2fb/tools/metrics/histograms/extract_histograms.py

The assigned owner "iburak@google.com" is not able to receive e-mails, please re-triage.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

I think jwd@ is doing the remainder of this work.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/1099dd84a847f237619490ee7701e17e26afe278

commit 1099dd84a847f237619490ee7701e17e26afe278
Author: Gayane Petrosyan <gayane@chromium.org>
Date: Tue Mar 20 20:35:39 2018

Add milestone format to histogram expiry.

Change "expiry_date" field to "expires_after" which now can be a date or
milestone.
Also change the date format to YYYY-MM-DD according to ISO8601 standard.

Bug:  744672 
Change-Id: Ic31c8c23e1e194f5e3c91148500b4598b1f259f2
Reviewed-on: https://chromium-review.googlesource.com/946866
Reviewed-by: Lei Zhang <thestig@chromium.org>
Reviewed-by: Jesse Doherty <jwd@chromium.org>
Commit-Queue: Gayane Petrosyan <gayane@chromium.org>
Cr-Commit-Position: refs/heads/master@{#544510}
[modify] https://crrev.com/1099dd84a847f237619490ee7701e17e26afe278/chrome/MAJOR_BRANCH_DATE
[modify] https://crrev.com/1099dd84a847f237619490ee7701e17e26afe278/chrome/browser/metrics/BUILD.gn
[modify] https://crrev.com/1099dd84a847f237619490ee7701e17e26afe278/components/metrics/generate_expired_histograms_array.gni
[modify] https://crrev.com/1099dd84a847f237619490ee7701e17e26afe278/tools/metrics/histograms/extract_histograms.py
[modify] https://crrev.com/1099dd84a847f237619490ee7701e17e26afe278/tools/metrics/histograms/generate_expired_histograms_array.py
[modify] https://crrev.com/1099dd84a847f237619490ee7701e17e26afe278/tools/metrics/histograms/generate_expired_histograms_array_unittest.py
[modify] https://crrev.com/1099dd84a847f237619490ee7701e17e26afe278/tools/metrics/histograms/print_style.py

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/240bab4594d5b3a4592d85be0352cc84286c4524

commit 240bab4594d5b3a4592d85be0352cc84286c4524
Author: Gayane Petrosyan <gayane@chromium.org>
Date: Thu Apr 12 09:31:00 2018

Add histogram expiration description.

Bug:  744672 
Change-Id: I738348739de70fb0fc4273bbe73a936b98520361
Reviewed-on: https://chromium-review.googlesource.com/1005791
Commit-Queue: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#550117}
[modify] https://crrev.com/240bab4594d5b3a4592d85be0352cc84286c4524/tools/metrics/histograms/histograms.xml

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a6ee443c0db6901c1fb9634e6397c9dc27fb60f4

commit a6ee443c0db6901c1fb9634e6397c9dc27fb60f4
Author: Gayane Petrosyan <gayane@chromium.org>
Date: Thu May 17 21:39:54 2018

Extended description for expired histograms.

Bug:  744672 
Change-Id: I419da9740e9844e648ac85ffce5783fb9fd1fecf
Reviewed-on: https://chromium-review.googlesource.com/1042375
Commit-Queue: Gayane Petrosyan <gayane@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#559687}
[modify] https://crrev.com/a6ee443c0db6901c1fb9634e6397c9dc27fb60f4/tools/metrics/histograms/README.md
[modify] https://crrev.com/a6ee443c0db6901c1fb9634e6397c9dc27fb60f4/tools/metrics/histograms/histograms.xml
[add] https://crrev.com/a6ee443c0db6901c1fb9634e6397c9dc27fb60f4/tools/metrics/histograms/one-pager.md