Header Cache Compression Feature

Options for compressing the header cache files

1. Support

Since: NeoMutt 2020-02-22

Dependencies: header cache

2. Introduction

The Header Cache Compression Feature can be used for speeding up the loading of large mailboxes. Also the space used on disk can be shrunk by about 50% - depending on the compression method being used.

The implementation sits on top of the header caching functions. So the header cache compression can be used together with all available database backends.

3. Variables

Table 16.1. Header Cache Compression Variables

Name Type Default
header_cache_compress_method string (empty)
header_cache_compress_level number 1

The header_cache_compress_method can be (empty) - which means, that no header cache compression should be used. But when set to lz4 , zlib or zstd - then the compression is turned on.

The header_cache_compress_level defines the compression level, which should be used together with the selected header_cache_compress_method. Here is an overview of the possible settings:

Table 16.2. Header Cache Compression Methods and it's Levels

Method Name Min Max
lz4 1 12
zlib 1 9
zstd 1 22

4. neomuttrc

# Example NeoMutt config file for the header cache compression feature.

# --------------------------------------------------------------------------
# VARIABLES – shown with their default values
# --------------------------------------------------------------------------
set header_cache_compress_level = 1
set header_cache_compress_method = ""

# vim: syntax=neomuttrc

5. Known Bugs


6. Credits

Tino Reichardt

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