I believe that tables' clustering factors are stored in pg_stats.correlation.
Here is how I came to this conclusion:
create table narrow_table as
with numbers as(
select generate_series as n from generate_series(0,1048575))
select n as seq_number,
(n/1024) + ((n%1024)<<10) as rand_number
from numbers;
alter table narrow_table
add constraint pk_narrow_table primary key(seq_number);
alter table narrow_table
add constraint unq_narrow_table unique(rand_number);
cluster narrow_table using pk_narrow_table;
vacuum full analyze narrow_table;
Now my table is physically ordered by its primary key. Apparently the
following query indicates that:
SELECT attname, correlation
FROM pg_stats
WHERE tablename LIKE '%narrow%';
"seq_number";1
"rand_number";0.00665399
Please correct me if I am wrong, or confirm my conclusion.
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