[Bug 1739672] [NEW] Regression in getaddrinfo(): calls block for much longer on Bionic (compared to Xenial)

[Mike Pontillo]

Public bug reported:

When testing MAAS on Bionic, we noticed sluggish performance that we
could not immediately explain.

After comparing the results from a run of the test suite on Xenial to a
run on Bionic, we determined that the slowdowns had to do with DNS
lookups. In particular, if MAAS attempts to resolve a hostname using
getaddrinfo() and the call fails, on Xenial the negative result is
returned in a fraction of a second. On Bionic, the negative result is
returned in ~1.6 seconds, according to some measures.

### To run the test ###

git clone https://github.com/mpontillo/test-getaddrinfo
cd test-getaddrinfo
make


### Results on Xenial ###
time ./test not-a-real-hostname
Trying to resolve: not-a-real-hostname
    getaddrinfo errno: Success
    getaddrinfo() return value: -2 (Name or service not known)

real	0m0.015s
user	0m0.000s
sys	0m0.000s


### Results on Bionic ###
$ time ./test not-a-real-hostname
Trying to resolve: not-a-real-hostname
    getaddrinfo errno: Resource temporarily unavailable
    getaddrinfo() return value: -3 (Temporary failure in name resolution)

real	0m1.609s
user	0m0.004s
sys	0m0.000s

** Affects: glibc (Ubuntu)
     Importance: Undecided
         Status: New

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: Incomplete

** Affects: systemd (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: xenial

** Also affects: systemd (Ubuntu)
   Importance: Undecided
       Status: New

** Also affects: glibc (Ubuntu)
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/1739672

Title:
  Regression in getaddrinfo(): calls block for much longer on Bionic
  (compared to Xenial)

Status in glibc package in Ubuntu:
  New
Status in linux package in Ubuntu:
  Incomplete
Status in systemd package in Ubuntu:
  New

Bug description:
  When testing MAAS on Bionic, we noticed sluggish performance that we
  could not immediately explain.

  After comparing the results from a run of the test suite on Xenial to
  a run on Bionic, we determined that the slowdowns had to do with DNS
  lookups. In particular, if MAAS attempts to resolve a hostname using
  getaddrinfo() and the call fails, on Xenial the negative result is
  returned in a fraction of a second. On Bionic, the negative result is
  returned in ~1.6 seconds, according to some measures.

  ### To run the test ###

  git clone https://github.com/mpontillo/test-getaddrinfo
  cd test-getaddrinfo
  make

  
  ### Results on Xenial ###
  time ./test not-a-real-hostname
  Trying to resolve: not-a-real-hostname
      getaddrinfo errno: Success
      getaddrinfo() return value: -2 (Name or service not known)

  real	0m0.015s
  user	0m0.000s
  sys	0m0.000s

  
  ### Results on Bionic ###
  $ time ./test not-a-real-hostname
  Trying to resolve: not-a-real-hostname
      getaddrinfo errno: Resource temporarily unavailable
      getaddrinfo() return value: -3 (Temporary failure in name resolution)

  real	0m1.609s
  user	0m0.004s
  sys	0m0.000s

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