TYPO3 Core

Here is a definition of index_section table:

CREATE TABLE index_section (
  phash int(11) DEFAULT '0' NOT NULL,
  phash_t3 int(11) DEFAULT '0' NOT NULL,
  rl0 int(11) unsigned DEFAULT '0' NOT NULL,
  rl1 int(11) unsigned DEFAULT '0' NOT NULL,
  rl2 int(11) unsigned DEFAULT '0' NOT NULL,
  page_id int(11) DEFAULT '0' NOT NULL,
  uniqid int(11) NOT NULL auto_increment,
  PRIMARY KEY (uniqid),
  KEY joinkey (phash,rl0),
  KEY page_id (page_id),
  KEY rl0 (rl0,rl1,phash),
  KEY rl0_2 (rl0,phash)
);

Indexes joinkey and rl0_2 differ only in the order of fields. MySQL does not need this, it can use index in queries regardless of field order without performace decrease. This duplicate index just takes more space on the disk and slows table down on insert/update operations.

(issue imported from #M3107)