# Engines, internals

## Postgres

* Write-Ahead Logging (WAL) mechanism for durability,&#x20;
* heap pages for table data,&#x20;
* B-tree or GiST indexes for efficient data retrieval.&#x20;
  * GiST (Generalized Search tree). GiST indexes are commonly used in PostgreSQL for indexing <mark style="background-color:orange;">spatial data</mark> (e.g., using the geometry type and associated operators), <mark style="background-color:orange;">full-text search</mark> (using the tsvector and tsquery types)



## Cassandra, HBase

memtable <> SSTable
