Re: CRCs

On Sunday 14 January 2001 04:49, Tom Lane wrote:

> A row-level CRC might be useful for this, but it would have to be on
> the data only (not the tuple commit-status bits).  It'd be totally
> impractical with a block CRC, I think.  To do it with a block CRC, every
> time you changed *anything* in a heap page, you'd have to find all the
> index items for each row on the page and update their copies of the
> heap block's CRC.  That could easily turn one disk-write into hundreds,
> not to mention the index search costs.  Similarly, a check value that is
> affected by tuple status updates would enormously increase the cost of
> marking tuples committed or dead.

Ah, finally. Looks like we are moving in circles (or spirals ;-) )Remember 
that some 3-4 months ago I requested help from this list several times 
regarding a trigger function that implements a crc only on the user defined 
attributes? I wrote one in pgtcl which was slow and had trouble with the C 
equivalent due to lack of documentation. I still believe this is that useful 
that it should be an option in Postgresand not a user defined function.

Horst