Re: progress report for ANALYZE

Hi Alvaro, vignesh,

I rebased the patch on 2a4d96eb, and added new column
"ext_compute_count" in pg_stat_progress_analyze vie to
report a number of computing extended stats.
It is like a "index_vacuum_count" in vacuum progress reporter or
"index_rebuild_count" in cluster progress reporter. :)

Please find attached file: v7.

And the following is a test result:
==============
[Session1]
\! pgbench -i
create statistics pg_ext1 (dependencies) ON aid, bid from pgbench_accounts;
create statistics pg_ext2 (mcv) ON aid, bid from pgbench_accounts;
create statistics pg_ext3 (ndistinct) ON aid, bid from pgbench_accounts;

[Session2]
# \a \t
# select * from pg_stat_progress_analyze ; \watch 0.0001

27064|13583|postgres|16405|initializing|f|0|0|0|0
27064|13583|postgres|16405|acquiring sample rows|f|16405|1640|0|0
27064|13583|postgres|16405|acquiring sample rows|f|16405|1640|23|0
27064|13583|postgres|16405|acquiring sample rows|f|16405|1640|64|0
27064|13583|postgres|16405|acquiring sample rows|f|16405|1640|1640|0
27064|13583|postgres|16405|computing stats|f|16405|1640|1640|0
27064|13583|postgres|16405|computing stats|f|16405|1640|1640|0
27064|13583|postgres|16405|computing extended stats|f|16405|1640|1640|0
27064|13583|postgres|16405|computing extended stats|f|16405|1640|1640|1
27064|13583|postgres|16405|computing extended stats|f|16405|1640|1640|2
27064|13583|postgres|16405|computing extended stats|f|16405|1640|1640|3
27064|13583|postgres|16405|finalizing analyze|f|16405|1640|1640|3

Note:
  The result on Session2 was shortened for readability.
  If you'd like to check the whole result, you can see attached file: "hoge.txt".
==============

Thanks,
Tatsuro Yamada