Documentation Home
MySQL Internals Manual

MySQL Internals Manual  /  Writing a Custom Storage Engine  /  Supporting Non-Sequential Reads

23.15 Supporting Non-Sequential Reads

In addition to table scanning, storage engines can implement methods for non-sequential reading. (Note: this is not "can" but rather a "must" because certain operations rely on proper implementation of position() and rnd_pos() calls. Two examples of such operations are multi-table UPDATE and SELECT .. table.blob_column ORDER BY something). The MySQL server uses these methods for certain sort operations.