Re: [HACKERS] mdnblocks is an amazing time sink in huge relations

> It seems to me that mdnblocks should assume that all segments
> previously verified to be of length RELSEG_SIZE are still of that
> length, and only do an _mdnblocks() call on the last element of the
> segment chain.  That way the number of kernel interactions needed
> is a constant independent of the number of segments in the table.
> (This doesn't make truncation of the relation by a different backend
> any more or less dangerous; we're still hosed if we don't get a
> notification before we try to do something with the relation.
> I think that is fixed, and if it's not this doesn't make it worse.)
> 
> Any objections?

Sounds great.  Now that the segments work properly, it is time for some
optimization.  Vadim has complained about the lseek() from day-1. 
Someday he wants a shared catalog cache to prevent that from being
needed.

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