![]() Now we'll read yet again the above paragraph taken from SQLite's own documentation, this time paying the due attention to any single world: The recently discovered issue is even worst (if possible) than the previous one: it will not simply cause a severe Spatial Index corruption, it could eventually transform any SQL query attempting to access the Spatial Index into a deadly slow query. If you missed this critical point, reading this old technical note is warmly suggested. You'll probably be well aware that not declaring an INTEGER PRIMARY KEY supporting any Geometry table could directly cause many severe Spatial Index releted headaches, e.g. If (for any reason) the above assumption is no longer satisfied then the Spatial Index will simply return unreliable and useless results. The SpatialLite's own implementation of the Spatial Index widely depends on ROWIDs in order to JOIN both the main table containing Geometries and the corresponding R*Tree table.Īnyway there is a dangerous hidden trap in all this: it works well only since ROWID values returned by the main table do exactly correspond to ROWID values stored into the R*Tree. Using ROWID values as relational keys whenever is possible is really useful in many SQL queries, because relational JOIN ops based on ROWIDs always are very efficient and fast to be resolved. In other words: a ROWID represents a Unique Identifier allowing to retrieve every individual row from a table in a very quick time. If the table has a column of type INTEGER PRIMARY KEY then that column is another Long as those names are not also used by explicitly declared columns. The rowid is always available as an undeclared column named ROWID, OID, or _ROWID_ as So you are kindly invited to carefully read this technical note.Įach entry in an SQLite table has a unique 64-bit signed integer key called the "rowid". The specific problem causing this issue seems to have a very low probability to happen under normal conditions anyway, once this problem will actually arise the consequences could easily have a really strong negative impact on the overall performance of SpatiaLite. By looking at the index, you can quickly identify page numbers based on the keywords.Broken R*Tree caused by shadowed ROWID issuesĪ new issue affecting the R*Tree Spatial Index has been recently reported. Imagine an index in the database like an index of a book. This helps SQLite quickly locate the row based on the values of the indexed columns. The index contains data from the columns that you specify in the index and the corresponding rowid value. Whenever you create an index, SQLite creates a B-tree structure to hold the index data. An index consists of one or more columns, but all columns of an index must be in the same table. How does an index workĮach index must be associated with a specific table. In addition, querying using equality (=) and ranges (>, >=, <,<=) on the B-tree indexes are very efficient. The B-tree keeps the amount of data at both sides of the tree balanced so that the number of levels that must be traversed to locate a row is always in the same approximate number. Note that B stands for balanced, B-tree is a balanced tree, not a binary tree. SQLite uses B-tree for organizing indexes. An index is an additional data structure that helps improve the performance of a query. Unlike a table, an index has an opposite relationship: (row, rowid). Therefore, you can consider a table as a list of pairs: (rowid, row). Each row also has a consecutive rowid sequence number used to identify the row. In the same time, each row has the same column structure that consists of cells. In relational databases, a table is a list of rows. Summary: in this tutorial, you will learn how to use SQLite indexes to query data faster, speed up sort operation, and enforce unique constraints.
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