> For the complete documentation index, see [llms.txt](https://amartyushov.gitbook.io/tech/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://amartyushov.gitbook.io/tech/databases/index/engines-internals.md).

# Engines, internals

## Postgres

* Write-Ahead Logging (WAL) mechanism for durability, 
* heap pages for table data, 
* B-tree or GiST indexes for efficient data retrieval. 
  * 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