Difference between Gaviota and Nalimov tablebases ?

[Ray]

Aprat from the obvious difference that there are no 6-men Gaviota tablebase available, how do Nalimov and Gaviota differ ? Why would an engine author choose one over the other ?

[Shaun]

Aprat from the obvious difference that there are no 6-men Gaviota tablebase available, how do Nalimov and Gaviota differ ? Why would an engine author choose one over the other ?

One reason, it is difficult to get permission to use the Nalimov TBs, explicit permission must be granted.

Shaun

[Ray]

One reason, it is difficult to get permission to use the Nalimov TBs, explicit permission must be granted.

Shaun

Yes I've heard that as well.

Technically I wonder what the differences are ?

[Shaun]

One reason, it is difficult to get permission to use the Nalimov TBs, explicit permission must be granted.

Shaun

Yes I've heard that as well.

Technically I wonder what the differences are ?

Sorry I have not looked at that yet!!! I am still waiting to test Gaviota on flash v disk - I only have 8gb flash drives on most my machines can't fit both TB formats...

Shaun

[mballicora]

One reason, it is difficult to get permission to use the Nalimov TBs, explicit permission must be granted.

Shaun

Yes I've heard that as well.

Technically I wonder what the differences are ?

Gaviota tablebases have the following advantages:

Smaller indexing memory (~10 MB vs. ~20MB)

More flexible compression options, from smaller memory requirement (6.5 GB) to faster decompression (may become the option of choice when Solid state disks become more popular). I believe this flexibility will be important in the future.

Better cache, which works like "bitbases on the fly". It is like having a cache with 4x more efficiency (in terms of memory).

Most importantly, it allows different ways to probe: "Soft", which only gets info from cache and does not go to HD (very fast), and "hard" (traditional= 1st cache, 2nd HD).
The engine can probe soft much more aggressively, almost everywhere. The traditional way has to be limited to places far from the leaves.

Also available are WDL probes. They are useful when what matters is whether the game is win, draw or loss, and not how may plies are needed to checkmate.
This increases the cache efficiency 4x (works like bitbases as mentioned above).

Miguel

[Ray]

Thanks Miguel.

Stockfish is a prime candidate for Gaviota tablebase support. I wonder if they will add it one day.