## Maintenance

To optimize page generation time, Piwigo uses cached information. For example, instead of counting the number of pictures contained in each category at each page reload, this information is stored in the database. In theory, this information should always be correct, but sometimes an error can occur and cached information becomes wrong.

Some informations become useless with time. Deleting this useless information from database make you save disk space.

- Nepovezane stavke: Prikaz slika koje nisu povezane ni s jednom nestvarnom skupinom.
- Slike istog naziva u više od jednoj stvarnoj skupini: Prikaz slika istog naziva koje se nalaze u više skupina.

- Update categories informations: For each category, informations to update or control are the following : list of parent categories, number of pictures, date of the last picture, position among brother categories, position among all categories. This action also checks the coherence of representative picture.
- Update photos information: For each picture, informations to update are : full path to file, average rate. Warning: do not get confuse with metadata informations which can be synchronized from Administration, Categories, Synchronize or by reaching the modification screen of a single picture (through Picture for example).
- Repair and optimize database: For each table, re-odrer, repair and optimize operations are done.

- Purge history detail: Delete all lines from `history` table. Screen Administration, Specials, History shows no informations anymore on past history. Warning: all data will be lost and there is no way to get informations back.
- Purge history summary: Delete all the summary information about visit history. This summary is calculated from the history detail.
- Purge sessions: Delete expired user sessions.
- Purge never used notification feeds
- Purge search history
- Purge compiled templates