SSTable

The tantivy-sstable crate is yet another sstable crate.

It has been designed to be used in quickwit:

• as an alternative to the default tantivy fst dictionary.
• as a way to store the column index for dynamic fast fields.

The benefit compared to the fst crate is locality. Searching a key in the fst crate requires downloading the entire dictionary.

Once the sstable index is downloaded, running a get in the sstable crate only requires a single fetch.

Right now, the block index and the default block size have been thought for quickwit, and the performance of a get is very bad.

Sorted strings?

SSTable stands for Sorted String Table. Strings have to be insert in sorted order.

That sorted order is used in different ways:

• it makes gets and streaming ranges of keys possible.
• it allows incremental encoding of the keys
• the front compression is leveraged to optimize the intersection with an automaton