[GRASS-user] Can I turn off compression

[Markus Metz]

Hi Ken,

turning off compression for all newly generated maps is indeed not
supported. If you don't care about disk usage and disk speed but processing
time, LZ4 is the compression method of choice. LZ4 compresses in near-real
time, i. e. in GRASS GIS there is no measurable CPU speed penalty, only
increased disk IO because more data need to be written and subsequently
read. I am using LZ4 myself as raster compression in workflows for
temporary intermediate maps and change the raster compression method before
writing out final results.

Currently, the default GRASS raster compression method can only be changed
with the environment variable GRASS_COMPRESSOR.

Markus M

On Sun, Mar 1, 2020 at 4:21 AM Vaclav Petras <wenzeslaus at gmail.com> wrote:
>
> Hi Ken,
>
> That sounds like a good experiment and I think there would be general
interest in what you find. However, please note that less compression may
not mean faster, because then there is more data to write and read and I/O
is generally a significant bottleneck. Markus Metz may say more about this
as he did tests when he was implementing the new compressions, but you
might be able to find some posts on this on the grass-dev mailing list.
>
> Best,
> Vaclav
>
> On Sat, Feb 29, 2020 at 11:40 AM Ken Mankoff <mankoff at gmail.com> wrote:
>>
>>
>> Hm. Answer: No
>>
>> I just did:
>>
>> export GRASS_COMPRESSOR=none
>>
>> And then get this error message:
>>
>> WARNING: No compression is not supported for GRASS raster maps, using
default ZLIB
>>
>> Seems like a shame to not have this as an option. I'll try speeding it
up by tweaking the compression method and amount.
>>
>>   -k.
>>
>> On 2020-02-29 at 08:37 -08, Ken Mankoff <mankoff at gmail.com> wrote...
>> > Hi,
>> >
>> > I'd like to turn off compression for all maps. Is this possible with
>> > g.gisenv or environment variables? The g.gisenv manual only shows how
>> > to choose among compression methods, not disable it.
>> >
>> > This does not seem to work:
>> >
>> > g.gisenv set="GRASS_COMPRESSOR=none" # optimize for speed
>> >
>> > I can decompress one map with:
>> >
>> > r.compress -u map=foo
>> >
>> > But I'm trying to skip the time spent compressing and decompressing
>> > altogether. I could use a small speed boost, and this seems like an
>> > easy way to speed things up - I can afford the disk space for all the
>> > temporary intermediate maps.
>> >
>> > Thanks,
>> >
>> >   -k.
>>
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