mahara-contributors team mailing list archive

["issam.taboubi" <issam.tab@xxxxxxxxx>]

Hi Robert,
 
I would like to share a solution that I applied in our institution.

We have a collection (66 pages) that takes 130 second to be copied
because of the method "update_hierarchy_path" doing update query on the
table "artefact" (in our case 500K records) , with no index in the query
it does not help.

We came up with the idea of adding the column owner in update query,
because we update the hierarchy of the path for the artifacts we just
inserted. And since there is an index on the owner column this has
lowered the processing from 139 seconds to 19 seconds.

Here are the two modified lines of code (line 1429 of artefact/lib.php):

$params = array($newparent->path, $length, $this->owner, $this->path, db_like_escape("{$this->path}/") . '%');
 $sql = "UPDATE {artefact} SET path = ? || SUBSTR(path, ?) WHERE  owner = ? AND (path = ? OR path LIKE ? )";

I want to know if there are any side effects for using the owner column
in the query.

Please advise

Thank you.

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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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