[Bizgres-general] Re: Latest bitmap patch results..

[Mark Kirkwood]

Ayush Parashar wrote:
> Results with the latest patch for size of bitmap index and performance 
> attached.
> In the attachment Jan 16 results represent the results with this patch.
> 

I thought it might be interesting to see what changes the latest patch 
brings, compared to those found by merely fixing the block packing.

Here is some results comparing:

1. Vanilla Bizgres Dec 15.
2. Patched bitmap.h to fix packing.
3. Latest patch that fixes bitmap.h, changes the tid -> block/offset 
mapping and introduces 8-bit words.

I'm using the same relation and queries from the block packing email.


Relation Sizes

          rel      |  pages(1) |  pages(2) |  pages(3)
------------------+-----------+-----------+---------
  bitmaptest_val0  |  18282    |  2105     |  1307
  bitmaptest_val1  |  18284    |  2106     |  1307
  bitmaptest_val2  |  51172    |  5918     |  2372

Query Execution

         query     | elapsed(1) | elapsed(2) | elapsed(3)
------------------+------------+------------+-------------
  3 bitmap scan    |   9        |  5         |  5
  2 bitmap scan    |   20       |  14        | 14
  1 bitmap scan    |   17       |  14        | 13

The latest patch almost halves the on-disk sizes again! however, its 
impact on query execution is about the same as the bitmap.h patch.

As has been noted previously, the next thing to look at is why a size 
reduction of 13-21 times is only giving a modest speedup of 1.4 to 1.8 
times (need to get out the profiler I guess....).

Cheers

Mark