page_compressed compressed page partially during import tablespace

The CREATE TABLE attribute page_compressed that was introduced in MariaDB 10.1.3 has no effect when innodb_doublewrite=0. This is because the actual compression only takes place within the doublewrite buffer code path.

The purpose of the doublewrite buffer is to guarantee crash-safety in the event that InnoDB is killed in the middle of a page write. Because it could become a performance bottleneck for write-heavy workloads, some users may choose to set innodb_doublewrite=0 and take the risk that crash recovery may fail. (The page should be referred to by the redo log, and a log checkpoint should not be made while a page write is still in progress, so the page corruption should be detected at InnoDB startup.)