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[Robert Lyon <robertl@xxxxxxxxxxxxxxx>]

** Changed in: mahara
    Milestone: 18.04.0 => 18.10.0

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https://bugs.launchpad.net/bugs/1427885

Title:
  Change "artefact.path" column to use the "nested set" technique for
  managing hierarchical data

Status in Mahara:
  Triaged

Bug description:
  Originally, we just had each artefact store its parent ID. This is
  slow because it requires running multiple queries to find all the
  descendants of a node.

  Then, we added a "path" element to each artefact. This is better, but
  you can't get a performance improvement by indexing the column,
  because most of the queries rely on the "LIKE" operator. (See
  https://bugs.launchpad.net/mahara/+bug/1423700 )

  So if we want to squeeze more performance out of this, I think the one
  remaining thing to look into is the "nested set" technique. This
  technique results in very fast searches for descendants, with the cost
  of somewhat slower writes. http://mikehillyer.com/articles/managing-
  hierarchical-data-in-mysql/

  There are even existing PHP libraries for using the technique, such as
  this one: http://www.sideralis.org/baobab/

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