1. Data can (already did) at any point, not only at specific, that you
marks by '!'.
2. If packed record doesn't fit into one page, control sequence is
parsed from end.
3. When rest of sequence will fit, compression is started again from
beginning.
4. If fragment has odd length, zero is added.
if you will generate compressed buffer instead control sequence, you can use
any compress/encoding schema.
If you will store this compressed buffer in one or more fragments is it
irrelevant.
You can join/splitting as you want. But for decompression you have to
collect all fragments into buffer.
Slavek
> 03.03.2016 18:34, Slavomir Skopalik wrote:
>> But value encoding cannot be implemented until we switch from fragment
>> compression to true record level compression.
> I was not speaking about any encoding, just about compacting the record.
>
> Fragments are not compressed independently. The whole record is being
> prepared for compression (control bytes are generated) and then splitted
> into multiple chunks accordingly to the control bytes, so that a single
> compressed sequence is not interrupted in the middle:
>
> 'aaaaoooiiiuee'
> {-4, 'a'} ! {-3, 'o'} ! {-3, 'i'} ! {1, 'u'} ! {2, 'ee'}
>
> This compressed sequence can be fragmented at any of the "!" points.
> This is needed to decompress them separately, without copying all the
> fragments into a single buffer before decompressing, i.e. fragment by
> fragment.
>
> But for the pack/unpack approach, we just copy data in chunks. Some
> field may have first N bytes stored in fragment 1 and the remaining M
> bytes stored in fragment 2. We know we need N+M bytes for the record. So
> we copy N bytes from fragment 1, release the page, fetch fragment 2 and
> continue copying N+1..M bytes into the record. Fragmenting is even
> easier than now, it can happen at any place.
>
> Am I missing something obvious?
>
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