Please execute me if I am using the wrong mailing list, but I ask the 
question in pgsql-admin, looks like no one know the answer.

we upgraded our pg db to 9.6, as we know, pg9.6 doesn't need full table scan in 
vacuum freeze.


so we think if we have run vacuum freeze on the table, and there is no change 
on table which has been vacuum freeze before  it should finish super faster.

However, it doesn't look like we expect. the next run of vacuum freeze still 
take long time. Then we run vacuum freeze with verbose. we notice it spends 
long time on scanning index.

it seems even all rows are frozen on the data page, vacuum freeze still needs 
to scan all the index pages. if we drop the index, then vacuum freeze finishes 

Does anyone know if it is true?

Btw, our table is large, and has about 40GB index files.  is there anyway to 
make the vacuum freeze faster in this case?

Thanks for the help.


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