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[Kristina Hoeppner <1724603@xxxxxxxxxxxxxxxxxx>]

** Changed in: mahara
    Milestone: None => 18.04.0

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https://bugs.launchpad.net/bugs/1724603

Title:
  update_hierarchy_path in artefacts/lib.php hammers sql when copying
  collections

Status in Mahara:
  Confirmed

Bug description:
  A teacher asked 40 students to copy a 15 page collection with numerous
  artefacts on each page, which crippled our mysql server.

  When testing it, even copying the collection once resulted in the web
  server timing out and raised the sql load incredibly.

  The code "update_hierarchy_path" in the artefact/lib.php on line 1423
  runs an sql query as below:

      `$sql = "UPDATE {artefact} SET path = ? || SUBSTR(path, ?) WHERE
  (path = ? OR path LIKE ? )";`

  The artefact table in Mahara does not index the `path` column, so
  whilst updating one artefact is not a major issue, but updating the
  path column for many artefacts hits the database massively.

  Indexing the path column (which is 1024 bytes) may not be a good
  solution long term, but either the query needs to be made more
  efficient or the column indexed.

  Mahara version 17.04_STABLE (updated about a month ago)
  Linux RHEL7
  MYSQL 5.6
  Browser is current chromium Version 61.0.3163.100 (but that is not relevant)

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