| PostgreSQL 8.0.1 Documentation | ||||
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48.3. Implementation
There are seven methods that an index operator class for GiST must provide:
- consistent
Given a predicate p on a tree page, and a user query, q, this method will return false if it is certain that both p and q cannot be true for a given data item.
- union
This method consolidates information in the tree. Given a set of entries, this function generates a new predicate that is true for all the entries.
- compress
Converts the data item into a format suitable for physical storage in an index page.
- decompress
The reverse of the
compressmethod. Converts the index representation of the data item into a format that can be manipulated by the database.- penalty
Returns a value indicating the "cost" of inserting the new entry into a particular branch of the tree. items will be inserted down the path of least
penaltyin the tree.- picksplit
When a page split is necessary, this function decides which entries on the page are to stay on the old page, and which are to move to the new page.
- same
Returns true if two entries are identical, false otherwise.
