I've a table with a large number (200 000 000) of records. I'd like to
remove ~90% of records from table that fulfill given criteria.

I know such operation can take a long time and I should backup and
restore database after operation has finished.

My question is, what is the most efficient way of performing such
operations. Should I put one delete statement into one transaction, or
divide it into few statements with seperate transactions?

Any help would be appreciated!

Kindly regards,
Kevin Smith