This change abstracts reading from on-disk data sources behind a single
reader which is then composed with memtable readers. This change also
abstracts all data sources behind a single reader obtained via
column_family::make_reader(). That reader is then used by algorithms
like column_family::for_all_partitions() or
column_family::query(). Having those abstractions will make it easier
to add row cache, because it will be encapsulated in a single place.
The "mutation_reader" defined in database.cc is a convenient mechanism
for iterating over mutations. It can be useful for more than just
database.cc (I want to use it in the compaction code), so this patch moves
the type's definition to mutation.hh, and the make_memtable_reader()
function to memtable::make_reader() (in memtable.hh).
Signed-off-by: Nadav Har'El <nyh@cloudius-systems.com>
* Forward commitlog replay_position to column_family.memtable, updating
highest RP if needed
* When flushing memtable, signal back to commitlog that RP has been dealt with
to potentially remove finished segment(s)
Note: since memtable flushing right now is _not_ explicitly ordered,
this does not actually work, since we need to guarantee ordering with
regards to RP. I.e. if we flush N blocks, we must guarantee that:
a.) We report "flushed RP" in RP order
b.) For a given RP1, all RP* lower than RP1 must also have been flushed.
(The latter means that it is fine to say, flush X tables at the same time, as long as we report a single RP that is the highest, and no lower RP:s exist in non-flushed tables)
I am however letting someone else deal with ensuring MT->sstable flush order.
Signed-off-by: Calle Wilund <calle@cloudius-systems.com>
Following what happened to others: we can now include memtable.hh
without including database.hh
Signed-off-by: Glauber Costa <glommer@cloudius-systems.com>
