Hi,

There seems to be a race condition when using mutiple archiver jobs on the same node.

Notice that the file is checked for existence before the filesize is checked.

Two archive jobs are started in a bash as such:

CONCURRENT_ARCHIVERS=2
  for i in $(seq 1 $CONCURRENT_ARCHIVERS)
  do
    (/var/www/console core:archive -vvv --concurrent-archivers=$CONCURRENT_ARCHIVERS) &
    pids+=($!)
  done

A few times a day, I get this error message for 1 of the 2 started processes:
WARNING [2020-04-27 03:39:26] 2654 /var/www/core/Filesystem.php(430): Warning - filesize(): stat failed for /var/www/tmp/climulti/archive.sharedsiteids.pid - Matomo 3.13.4. I'm not able to forcefully reproduce it, but we know if happens a few times a day since we get a notification if a archive process exits with non-zero code.

We only see this in our test environment, which has many sites but no new stats added to the sites. Run time for each archive job is <3s.

I looked through the code, and the only thing that I could spot as a potential source is this:

Is there something there, where if running multiple archivers that completes in less than 5s, where this can cause issues ?

I don't have a suggestion for a fix now. Attached the output from the archive processes that runs, where one of them (b) is giving a WARNING
a.log
b.log