Motivation

When reading from many possibly large files in a fashion similar to random access, it is usually the fastest and most efficient to use memory maps.

Although memory maps have many advantages, they represent a very limited system resource as every map uses one file descriptor, whose amount is limited per process. On 32 bit systems, the amount of memory you can have mapped at a time is naturally limited to theoretical 4GB of memory, which may not be enough for some applications.

Limitations

System resources (file-handles) are likely to be leaked! This is due to the library authors reliance on a deterministic __del__() destructor.
The memory access is read-only by design.

Overview

Smmap wraps an interface around mmap and tracks the mapped files as well as the amount of clients who use it. If the system runs out of resources, or if a memory limit is reached, it will automatically unload unused maps to allow continued operation.

To allow processing large files even on 32 bit systems, it allows only portions of the file to be mapped. Once the user reads beyond the mapped region, smmap will automatically map the next required region, unloading unused regions using a LRU algorithm.

Although the library can be used most efficiently with its native interface, a Buffer implementation is provided to hide these details behind a simple string-like interface.

For performance critical 64 bit applications, a simplified version of memory mapping is provided which always maps the whole file, but still provides the benefit of unloading unused mappings on demand.

Prerequisites

Python 3.7+
OSX, Windows or Linux

The package was tested on all of the previously mentioned configurations.

Installing smmap

Its easiest to install smmap using the pip program:

$ pip install smmap

As the command will install smmap in your respective python distribution, you will most likely need root permissions to authorize the required changes.