Re: Quick-and-dirty compression for WAL backup blocks

Hi all,

I examined the effect of block-hole compression patch.

I compared the amounts of writing of the WAL data of CVS(7/11) and
8.0.3. (The amount of the WAL data writing was measured by the number of
executions of the write() function in XLogWrite().)
And, I measured the size of the hole.

Environment;
IBM x206 P4 3.0GHz Mem 4GB
CentOS 4.0 (Linux 2.6.9-5.0.3.ELsmp)

Parameters;
shared_buffers = 65535
checkpoint_segments = 30
default_with_oids = false (8.0.3)
default_with_oids = off   (CVS)

How to exam;
0) initdb --no-locale
1) pgbench -i -s 100 pgbench
2) pgbench -n -c 50 -t 5000 pgbench
3) vacuumdb -d pgbench
4) pgbench -n -c 50 -t 5000 pgbench

Results;    |    8.0.3    |                  CVS(7/11)
Exam |         |   |         |   |        block-hole (byte)    |  write  |C.P|  write  |C.P|   total   | min | max  |
avg
-----+---------+---+---------+---+-----------+-----+------+---------1)  |  187505 | 3 |  187373 | 4 |    194056 |  36 |
8124| 3881.122)  |  509725 | 6 |  513489 | 5 | 115564476 |  12 | 8096 |  347.693)  |  280456 | 2 |  172973 | 2 |
95923360| 248 | 8156 |  614.084)  |  533971 | 7 |  525135 | 6 | 171147256 |  12 | 8140 |  482.11
 

C.P = Checkpoint frequency

It has been understood that patchs seems to be effective at VACUUM as a
result of the measurement. But, in other cases, the effect was not so seen.



-- 
Junji Teramoto