Full_Name: Ben Trask Version: OS: URL: ftp://ftp.openldap.org/incoming/ Submission from: (NULL) (192.241.251.11)
Hi, Transaction commits are one of the few bottlenecks in MDB, because it has to fsync twice, sequentially. I think MDB could support mixed low and high durability transactions in the same database by adding per-page checksums and a third root page. The idea is that when committing a low-durability transaction, no fsyncs are performed. One of the two other roots is always consistent on-disk to serve as a "backstop" in the event of power loss/kernel panic. The two other pages are allowed to alternate, with consistency only ensured by checksums. During a restore after a crash, the non-durable roots (if any) get compared against the third durable root. Any new pages get checksum'd to ensure integrity. In the worst case, the durable root is used.
