The sstable_writer_config creation looks simple (just declare
the struct instance) but behind the scenes references storage
and feature services, messes with database config, etc.
This patch teaches the sstables_manager generate the writer
config and makes the rest of the code use it. For future
safety by-hands creation of the sstable_writer_config is
prohibited.
The manager is referenced through table-s and sstable-s, but
two existing sstables_managers live on database object, and
table-s and sstable-s both live shorter than the database,
this reference is save.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
The latter creates the config by hands, but the plan is to
create it via sstables_manager. Callers of this helper are the
final frontiers where the manager will be safely accessible.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
This commit makes database, sstables and tests aware
of which large_partition_handler they use.
Proper large_partition_handler is retrievable from config information
and is based on existing compaction_large_partition_warning_threshold_mb
entry. Right now CQL TABLE variant of large_partition_handler is used
in the database.
Tests use a NOP version of large_partition_handler, which does not
depend on CQL queries at all.
thread_scheduling_groups are converted to plain scheduling_group. Due to
differences in initialization (scheduling_group initializtion defers), we
create the scheduling_groups in main.cc and propagate them to users via
a new class database_config.
The sstable writer loses its thread_scheduling_group parameter and instead
inherits scheduling from its caller.
Since shares are in the 1-1000 range vs. 0-1 for thread scheduling quotas,
the flush controller was adjusted to return values within the higher ranges.
This came from Avi's review on the read_monitors. He suggests we
wouldn't keep shared pointers, and would instead have the caller
ensuring lifetime. That makes sense, but having the writer interface
using shared_ptr and the read interface using references would lead to
an inconsistent interface.
For the sake of consistency we will change the write monitor to take
references before we do that. From database.cc's perspective, we could
now keep the monitors in a do_with() block, but we will keep the
shared_ptrs to manage their lifetime in anticipation of upcoming patches
in this series, where we'll have to pass them somewhere else.
Signed-off-by: Glauber Costa <glauber@scylladb.com>
There is no need to include the whole sstables.hh file in
memtable-sstable.hh anymore. All we need is the shared_sstable
definition and the progress monitor.
Signed-off-by: Glauber Costa <glauber@scylladb.com>
Right now we pass a permit to the memtable writer and that permit is
used insite write_memtable_to_sstable to compose a write_monitor.
We would like to extend the write_monitor to include other things, that
right now are not available as parameters to write_memtable_to_sstable -
and which are possibly too specialized to be.
The solution for that is to pass the write_monitor instead of the permit
to the writer. Conceptually, that also makes sense because the
write_monitor is something the sstable writer is aware of. Permits, on
the other hand, are a database concept that is alien to the sstable
writer.
Signed-off-by: Glauber Costa <glauber@scylladb.com>
Message-Id: <20170915032836.21154-1-glauber@scylladb.com>
This allows a queued flush to start while we fsync the current
sstable, which helps reduce the overall time new writes are blocked on
dirty memory.
Signed-off-by: Duarte Nunes <duarte@scylladb.com>
This allows a queued flush to start while we fsync the current
sstable, which helps reduce the overall time new writes are blocked on
dirty memory.
Signed-off-by: Duarte Nunes <duarte@scylladb.com>
In scylla, we have foreground processes, which are latency sensitive and
need to be responded to as fast as possible in order to maintain good
latency profiles, and background process, which are less so.
The most important background processes we have during normal write
workload operations are memtable writes and sstable compactions. Those
processes are quite CPU-intensive, and left unchecked will easily
dominate the CPU. Lower values of task-quota usually help, as it will
force those processes to preempt more, but aren't enough to guarantee
good isolation. We have seen boxes with good NVMe storage having their
throughput reduced to less than half of the original baseline in a short
dive down for the duration of a compaction.
In the long run, our goal is to leverage the CPU scheduler to make sure
that those processes are balanced with respect to all the others.
However, the current state of affairs is causing grievances as this very
moment. Thankfully, those processes live in a seastar::thread, that
ships with its own rudimentary bandwidth control mechanism: the
scheduling group.
The goal of this patch is to wrap background processes together in a
scheduling group, and assign to such group 50 % of our CPU power; the
remainder being left to foreground processes.
While we pride ourselves in dynamically adjusting things to the
workload, we won't be able to do this properly before the CPU scheduler
lands - and let's face it, leaving background processes run wild is not
adaptative either. Every workload would benefit most from a different
value for such shares, but 50 % is as fair as it gets if we really need
static partitining in the mean time.
As a defense against unforeseen consequences, we'll leave the actual
value as an option, but will do our best to hide it - as this is not a
tunable that we want to be part of a normal Scylla setup. The most
convenient place for this tunable is still db::config, so we can easily
pass it down to the database layer - but we will not document it in the
yaml, and will clearly note in the help string that it is not supposed
to be tuned.
Signed-off-by: Glauber Costa <glauber@scylladb.com>
