mahara-contributors team mailing list archive

[Robert Lyon <robertl@xxxxxxxxxxxxxxx>]

Hi Brian,

Good point about the missing index on the path column.

The first thing I'd try is adding a unique index to the 'path' column as
each path should be unique as they all end with the id of the artefact
itself and that is unique.

The purpose of the 'path' column (if I remember right) is to handle the
hierarchy issue where the child items are older (lower id) than the
parent items. Eg if some files are uploaded then some folders are made
and the files are moved into the folders we could end up with paths like

2/5/192/16
2/5/192/412
2/5/193/6
2/5/193/77

which were complicated to sort correctly with just the 'id' and 'parent'
columns

It might make sense to have a 'artefact_path_structure' table to handle
things instead of the 'path' column in the future.

Cheers

Robert

** Changed in: mahara
       Status: New => Confirmed

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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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