[GRASS-dev] [GRASS GIS] #2750: LZ4 when writing raster rows; better than double I/O bound r.mapcalc speed

[GRASS GIS]

#2750: LZ4 when writing raster rows; better than double I/O bound r.mapcalc speed
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  Reporter:  sprice       |      Owner:  grass-dev@…
      Type:  enhancement  |     Status:  new
  Priority:  normal       |  Milestone:  7.1.0
 Component:  Raster       |    Version:  svn-trunk
Resolution:               |   Keywords:  ZLIB LZ4 ZSTD
       CPU:  OSX/Intel    |   Platform:  MacOSX
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Comment (by neteler):

 '''To summarize the current state'''

 We currently have the following compression methods in trunk (according to
 lib/gis/compress.c; set by `export GRASS_COMPRESSOR=XXX`):

  * `NONE` (uncompressed)
  * `RLE`  (generic Run-Length Encoding of single bytes)
  * `ZLIB` (DEFLATE, good speed and compression)
    * with zlib compression levels (`export GRASS_ZLIB_LEVEL=X`): -1..9 (-1
 is default which is level 6)
    * Notes from #comment:23: ZLIB level = 0 tells ZLIB to copy the data as
 is from source to destination. With CELL maps, the rasterlib will then
 still trim high zero bytes with trim_bytes() which can already reduce the
 data size considerably, but ZLIB will not compress the data.
  * `LZ4`  (fastest, low compression)
  * `BZIP2` (slowest, high compression)

 NULL file compression: At time it must be explicitly turned on (IMHO it
 should become the default) with
  * `export GRASS_COMPRESS_NULLS=1`

 Backward NULL file compression compatibility could be implemented in
 relbranch70 only by ZLIB's DEFLATE (see #comment:36). Hence ZLIB may
 qualify for the default NULL compression algorithm.

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Ticket URL: <https://trac.osgeo.org/grass/ticket/2750#comment:40>
GRASS GIS <https://grass.osgeo.org>