If we're operating on the freelist, see if our current pghead
can satisfy the request before giving up and using new pages.

Howard Chu authored 12 years ago and Quanah Gibson-Mount committed 12 years ago

Better handling of missing entries

Treat zero-length entries properly (as missing entries) in entry_next()
and entry_get_int().

Howard Chu authored 12 years ago and Quanah Gibson-Mount committed 12 years ago

Lightning Memory-Mapped Database

Howard Chu authored 12 years ago and Quanah Gibson-Mount committed 12 years ago

Since MDB writes are fully serialized in txn_begin, we can use CSNs as
commit sequence numbers, not just change sequence numbers. This will
prevent most instances of out-of-order writes, so syncprov will almost
never need to transmit a change without a cookieCSN. (Out-of-order is
still possible, if the write was received via syncrepl.)

Was leaving it 0 initially.

Use the latest meta page

Allow both increasing and decreasing the environment size.
But don't allow decreasing below the currently occupied space.

These ops could fail if the map is full.

Don't try to reclaim overflow pages while operating on
the freelist (for now). The circular dependencies are much like
the single-page case, but worse. Maybe look into this in the
future, but it's not absolutely necessary now.

Keep list sorted if it grows during a write. Don't free pghead until
we're sure our writes are all finished.