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[Kristina Hoeppner <1450676@xxxxxxxxxxxxxxxxxx>]

** Tags added: performance

** Changed in: mahara
   Importance: Undecided => Medium

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https://bugs.launchpad.net/bugs/1450676

Title:
  The way we add new columns to tables can cause db to lock up

Status in Mahara:
  Confirmed

Bug description:
  Currently when we want to add a column to an existing table we do
  something like this in lib/db/upgrade.php

  $table = new XMLDBTable('group');
  $field = new XMLDBField('allowarchives');
  $field->setAttributes(XMLDB_TYPE_INTEGER, 1, null, XMLDB_NOTNULL, null, null, null, 0);
  add_field($table, $field);

  The problem is if the database is big it can cause things to lock up

  Changing the above to a more direct:
  execute_sql('ALTER TABLE {group} ADD COLUMN allowarchives SMALLINT NOT NULL DEFAULT 0');

  seems to avoid this problem.

  So this bug is here so we can find out why the current way is so
  resource intensive and/or what dangers there are doing it the more
  direct way.

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