[Rd] Compression (really about LazyDate)

[Therneau, Terry M., Ph.D.]

Thank you Brian.   I had not quite grasped how the process works, now the descriptions and 
usage make sense.

Terry


On 2/19/21 4:28 AM, Prof Brian Ripley wrote:
> On 18/02/2021 18:30, Therneau, Terry M., Ph.D. via R-devel wrote:
>> This is a CRAN question:
>>
>> I have taken care to compress files in the data directory using "xz" (and checked that it
>> is the best).  Is there then any impact or use for the LazyDataCompression option in the
>> DESCRIPTION file?
>>
>
> I have difficulty comprehending that, so I will try to answer my guess at what you meant 
> to ask.
>
> What LazyDataCompression does is completely separate from the contents of the data 
> directory.  As the manual say
>
> <quote>
> Some packages using ‘LazyData’ will benefit from using a form of compression other than 
> gzip in the installed lazy-loading database. This can be selected by the --data-compress 
> option to R CMD INSTALL or by using the ‘LazyDataCompression’ field in the DESCRIPTION 
> file. Useful values are bzip2, xz and the default, gzip. The only way to discover which 
> is best is to try them all and look at the size of the pkgname/data/Rdata.rdb file.
> </quote>
>
> When a package is installed with LazyData (and you neglected to tell us if that is the 
> case), the datasets in the data directory are loaded (and hence decompressed), and 
> stored in a database. For a LazyData package the compression used in the data directory 
> only affects the source package size (I guess your criterion for 'best') and how fast it 
> is installed (rarely a consideration but there have been LazyData packages where 
> installing the data takes most of the time).  At run-time only the compression specified 
> by LazyDataCompression is relevant.
>


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