jldugger on Tarsnap performance issues in late March, most of April

Comment on Tarsnap performance issues in late March, most of April parent

We actually have our Chef rdiff backup cookbook randomly distribute jobs across a buckets of time using a hash function of the hostname.

sillysaurus3 11y

I have to know: Why a hash function of the hostname?

pliu 11y

The chef-client cookbook does a similar thing in its cron recipe:

  # Generate a uniformly distributed unique number to sleep.
  if node['chef_client']['splay'].to_i > 0
    checksum   = Digest::MD5.hexdigest(node['fqdn'] || 'unknown-hostname')
    sleep_time = checksum.to_s.hex % node['chef_client']['splay'].to_i
  else
    sleep_time = nil
  end

https://github.com/opscode-cookbooks/chef-client/blob/master...

This is random enough so you won't kill the server, and deterministic so the resource isn't always changing every Chef run.

toomuchtodo 11y

No hash collisions, hostnames (in almost all practical environments) are never identical.

jldugger 11y

It's more or less random, but stable.

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