Memory Mapped file segment / always appending

[Johannes Lichtenberger]

To be fair, I don't know how to truncate it directly with Panama.

I'm currently using the FileChannel API just for truncating during closing:

try (final FileChannel outChan = new
FileOutputStream(dataFile.toFile(), true).getChannel()) {
  outChan.truncate(dataSegmentFileSize);
} catch (IOException e) {
  throw new SirixIOException(e);
}


But I guess it's also more of a conceptual issue (or should truncating be
pretty fast?).

I've committed the file:
https://github.com/sirixdb/sirix/blob/master/Screenshot%20from%202020-07-27%2018-58-39.png

kind regards
Johannes

Am Mo., 27. Juli 2020 um 19:18 Uhr schrieb Maurizio Cimadamore <
maurizio.cimadamore at oracle.com>:

>
> On 27/07/2020 18:12, Johannes Lichtenberger wrote:
> > Hi,
> >
> > as I'm always appending data to the end of a file. I came up with the
> idea
> > to always map a segment in chunks of Integer.MAX, that is the segment
> > always get's closed and a new segment gets created with twice the size
> (for
> > reading/writing). When I'm closing the writer I'm simply truncating the
> > file(s) to the real length.
> >
> > However, I just saw that it's horribly slow for a lot of small writes.
> That
> > is I'm always creating a read/write page reader, and closing it again
> after
> > a write. However, truncating a lot of unused space, over and over again
> is
> > a real problem. I've attached a flame graph from YourKit showing that
> half
> > of the time over a large amount of CPU samples is spend with truncating.
>
> Is the time spent in the Panama API, or do you mean that the code is
> slow just natively (e.g. at the mmap level)
>
> We can't see the attachment (the server truncates them :-) )
>
> Maurizio
>
> >
> > Any ideas, how to improve performance?
> >
> > The packe is this and very small:
> >
> >
> https://github.com/sirixdb/sirix/tree/master/bundles/sirix-core/src/main/java/org/sirix/io/memorymapped
> >
> > kind regards
> > Johannes
>