Gavin Sherry wrote:
Hi all,

Attached is a patch implementing bitmap indexes. It includes major
enhancements on the patch submitted during feature freeze for 8.2 here[1].

In particular: much better integration with the existing bitmap scan code
with the internals of the bitmap streaming pushed down into the AM and
hidden from the executor code; completely new index creation algorithm
which reduced creation time by 20-75% depending on the data; modifications
to the encoding mechanism to suit the integration with bitmap index scans;
work on memory management; lots of code rewriting; range query support.
The code is also much cleaner now.

Thanks! I'll take a look at it.

We need to give the indexam API some further thought. As you know, I've
been working on the Grouped Index Tuples stuff, which also requires
changes to the API to get full benefit. There's a bunch of functionality
I'd like to see:

* Support for streamed bitmaps, like you have implemented.

* Support for candidate matches. This is needed for GIT, as well as
range-encoded bitmap indexes if/when we add them.

* Support for returning tuples in partial order. This is again needed for GIT, because grouped tuples don't keep track of the ordering within the group, so they need to be sorted if ordering necessary. And again it's also useful to return tuples in order from range-encoded bitmaps.

* Support for kill_prior_tuple on bitmap scans.

* A bulk insert API. When inserting a lot of tuples with similar keys, we could a considerable amount of CPU with a bulk insert API. A bulk insert to a B-tree for example would only need to descend the tree once, find the insert location, lock the target page just once and insert all the tuples that belong to that page. That would potentially also reduce WAL traffic.

There are still some things Jie and I have not gotten to yet:

o Improving VACUUM support -- currently, VACUUM FULL means REINDEX for
  bitmaps. Heikki Linnakangas offered to work on this. Heikki, are you
  still interested?

Yeah, I can look into that.

o Test WAL replay more thoroughly.

I've had that problem too with a lot of things I've hacked. I've used a shell script that does the operation under test, runs a select, kills and restarts postmaster, and reruns the select. If the select after crash returns the same result as before, presumably WAL code works. But you need to watch out for full page writes that might mask bugs in the redo code.

Anyone have a more sophisticated method?

  Heikki Linnakangas

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