Increase share size to 512 bytes

[adlerjohn]

I like big blocks and I cannot lie.

Change ShareSize to 512: https://github.com/celestiaorg/celestia-core/blob/c193de698f889a3c78565ac4a73899326a23d544/pkg/consts/consts.go#L15

This will also require a change to the reserved bytes to 2: https://github.com/celestiaorg/celestia-core/blob/c193de698f889a3c78565ac4a73899326a23d544/pkg/consts/consts.go#L21

[musalbas]

Why would this require a change to the reserved bytes to 2?

[adlerjohn]

If the reserved byte(s) points to the first byte of the message, it needs to be able to contain [0, 511]. With one byte it can only contain [0, 255].

[rootulp]

We want to do this as a fast follow after #659

[rootulp]

Based on synchronous discussion, this issue needs investigation to determine what the share size should be.

[evan-forbes]

to help figure out what breaks, we are doing #825 first, which could potentially be merged and close this issue

[musalbas]

ODS	256 byte shares	512 byte shares	1024 byte shares
4	53 MB/s	95 MB/s	169 MB/s
8	116 MB/s	203 MB/s	297 MB/s
16	208 MB/s	367 MB/s	540 MB/s
32	265 MB/s	478 MB/s	697 MB/s
64	300 MB/s	540 MB/s	745 MB/s
128	305 MB/s	534 MB/s	695 MB/s
256	293 MB/s	496 MB/s	634 MB/s
512	276 MB/s	458 MB/s	612 MB/s

512x512 blocks with:

• 256 byte shares: 67 MB
• 512 byte shares: 134 MB
• 1024 byte shares: 268 MB

[rootulp]

#850 merged so this issue seems close-able. In the spirit of:

I like big blocks and I cannot lie.

if we can increase share size to 1024 bytes then can we please create a new issue to tackle that?