Gregory Stark wrote:
"Heikki Linnakangas" <[EMAIL PROTECTED]> writes:

Let's use a normal hash table instead, and use a lock to protect it. If we only
update it every 10 pages or so, the overhead should be negligible. To further
reduce contention, we could modify ReadBuffer to let the caller know if the
read resulted in a physical read or not, and only update the entry when a page
is physically read in. That way all the synchronized scanners wouldn't be
updating the same value, just the one performing the I/O. And while we're at
it, let's use the full relfilenode instead of just the table oid in the hash.

It's probably fine to just do that. But if we find it's a performance
bottleneck we could probably still manage to avoid the lock except when
actually inserting a new hash element. If you just store in the hash an index
into an array stored in global memory then you could get away without a lock
on the element in the array.
It starts to get to be a fair amount of code when you think about how you
would reuse elements of the array. That's why I suggest only looking at this
if down the road we find that it's a bottleneck.

Another trick you could do is to use acquire the lock conditionally when updating it. But I doubt it's a problem anyhow, if we put some sane lower limit in there so that it's not used at all for small tables.

  Heikki Linnakangas

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