Allow to make a streaming reader with a vector of ranges in addition to
a single range. This will be used soon in following streaming patch.
We can make the reader more efficient later.
The procedure to calculate max purgeable timestamp is optimized
by only visiting sstables that overlap with key being currently
compacted. That's done using incremental sstable selector.
Function to calculate maximum purgeable timestamp is made 10 times
faster when compacting sstables overlap with 10% of all sstables.
Fixes#1322.
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
The implementation assumes that memtable's region group is owned by
dirty_memory_manager, and tries to obtain a reference to it like this:
boost::intrusive::get_parent_from_member(_region.group(), &dirty_memory_manager::_region_group));
This is undefined behavior when the region's group does not come from
dirty manager. It's safer to be explicit about this dependency by
taking a reference to dirty_memory_manager in the constructor.
Streaming memtable have a delayed mode where many flushes are coalesced
together into one, with the actual flush happening later and propagated
to all the previous waiters.
However, the timer that triggers the actual flush was not using the
newly introduced flush infrastructure. This was a minor problem because
those flushes wouldn't try to take the semaphore, and so we could have
many flushes going on at the same time.
What was a potential performance issue became a correctness issue when
we moved the reversal of the dirty memory accounting out of
revert_potentially_cleaned_up_memory() into remove_from_flush_manager().
Since the latter is only called through the flush infrastructure, it
simply wasn't called. So the deferral of the reversal exposed this bug.
Signed-off-by: Glauber Costa <glauber@scylladb.com>
Message-Id: <0d5755375bc27524b8cfb9970c76d492b14d9eea.1480522742.git.glauber@scylladb.com>
New sstables are loaded and added in parallel, meaning that scylla can
potentially return stale data if a new sstable containing a tombstone
wasn't loaded yet. Compaction should also not run until all new sstables
are added for similar reasons.
Fix is about separating blocking and non-blocking steps to allow
atomic add of multiple new sstables.
Fixes#1368.
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
Message-Id: <14283b8a4a69127071d1fabef320a93c91817ec2.1480356073.git.raphaelsc@scylladb.com>
"We currently write the size_estimates system table for every schema
on a periodic basis, currently set to 5 minutes, which can interfere
with an ongoing workload.
This patchset virtualizes it such that queries are intercepted and we
calculate the results on the fly, only for the ranges the caller is interested in.
Fixes#1616"
* 'virtual-estimates/v4' of github.com:duarten/scylla:
size_estimates_virtual_reader: Add unit test
db: Delete size_estimates_recorder
size_estimates: Add virtual reader
column_family: Add support for virtual readers
storage_service: get_local_tokens() returns a future
nonwrapping_range: Add slice() function
range: Find a sequence's lower and upper bounds
system_keyspace: Build mutations for size estimates
size_estimates: Store the token range as bytes
range_estimates: Add schema
murmur3_partitioner: Convert maximum_token to sstring
When we finish writing a memtable, we revert the dirty memory charges
immediately. When we do that, dirty memory will grow back to what it
was, and soon (we hope) will go down again when we release the requests
for real.
During that time, we may not accept new requests. Sealing can take a
long time, specially in the face of Linux issues like the ones we have
seen in the past. It also will take proportionally more time if the
SSTables end up being small, which is a possibility in some scenarios.
This patch changes the dirty_memory_manager so that the charges won't be
reverted right after we finish the flush. Rather, we will hold on to it,
and revert it right before we update the cache. We don't need to do it
for all classes of memtable writes, because after we finish flushing,
flush_one() will destroy the hashed element anyway.
Signed-off-by: Glauber Costa <glauber@scylladb.com>
Message-Id: <2d5a8f6ca57d5036f4850ac163557bca59b8063d.1480004384.git.glauber@scylladb.com>
We current pass a region group to the memtable, but after so many recent
changes, that is a bit too low level. This patch changes that so we pass
a memtable list instead.
Doing that also has a couple of advantages. Mainly, during flush we must
get to a memtable to a memtable_list. Currently we do that by going to
the memtable to a column family through the schema, and from there to
the memtable_list.
That, however, involves calling virtual functions in a derived class,
because a single column family could have both streaming and normal
memtables. If we pass a memtable_list to the memtable, we can keep
pointer, and when needed get the memtable_list directly.
Not only that gets rid of the inheritance for aesthetic reasons, but
that inheritance is not even correct anymore. Since the introduction of
the big streaming memtables, we now have a plethora of lists per column
family and this transversal is totally wrong. We haven't noticed before
because we were flushing the memtables based on their individual sizes,
but it has been wrong all along for edge cases in which we would have to
resort to size-based flush. This could be the case, for instance, with
various plan_ids in flight at the same time.
At this point, there is no more reason to keep the derived classes for
the dirty_memory_manager. I'm only keeping them around to reduce
clutter, although they are useful for the specialized constructors and
to communicate to the reader exactly what they are. But those can be
removed in a follow up patch if we want.
The old memtable constructor signature is kept around for the benefit of
two tests in memtable_tests which have their own flush logic. In the
future we could do something like we do for the SSTable tests, and have
a proxy class that is friends with the memtable class. That too, is left
for the future.
Fixes#1870
Signed-off-by: Glauber Costa <glauber@scylladb.com>
Message-Id: <811ec9e8e123dc5fc26eadbda82b0bae906657a9.1479743266.git.glauber@scylladb.com>
Virtual readers allow queries to selected tables, usually system
tables, to be answered by the engine. This is useful for tables which
aren't written by users and whose contents can be calculated on
demand.
Signed-off-by: Duarte Nunes <duarte@scylladb.com>
This patch addresses post-merge follow up comments by Tomek.
Basically, what we do is:
- we don't need to signal() from remove_from_flush_manager(), because
the explicit flushes no longer wait on the condition variable. So we
don't.
- We now wait on the stop() flushes (regardless of their return status)
so we can make sure that the _flush_queue will indeed be done with.
- we acquire the semaphore before shutting down the dirty_memory_manager
to make sure that there are no pending flushes
- the flush manager that holds the semaphore has to match in the exception
handler
Signed-off-by: Glauber Costa <glauber@scylladb.com>
Message-Id: <a23ab5098934546c660a08de64cd9294bb3a2008.1479400239.git.glauber@scylladb.com>
The way we currently flush memtables, we seal the current one but wait
on a semaphore for the actual flush to proceed.
This is pointless, because if the flush is not proceeding we'll use up
memory for the new entries anyway, be them in a newly opened memtable or
not. As a matter of fact, by opening a new memtable we are foregoing
coalescing opportunities.
After recent changes to the flush paths, we are now in a position to do
differently. We move the semaphore earlier, and if we can't acquire it
we keep appending to the current memtable.
For explicit flushes, we'll queue and prioritize them over memory-based
flushes. This has the nice property of potentially coalescing various
flushes for the same CF into one.
Coalescing flushes for the same CF is particularly helpful for
commitlog-initiated flushes that can't complete within the flush period.
What we see currently, is that under heavy load the commitlog will keep
sealing memtables adding to the existing load.
Another interesting property of this approach is that we can keep the
disk utilization higher, by allowing a new flush to start before the
memtable is fully sealed. By design, every time a memtable is finished
flushing it will call revert_potentially_cleaned_up_memory() to revert
the virtual memory charges. That is the perfect moment for us to act.
It indicates that all the data flushing part is done.
The way we'll do it is by keeping the semaphore_units alive for this
memtable. When the flush ends, we destroy that object. This will
effectively trigger the next flush if there is a next flush that can be
initiated.
Signed-off-by: Glauber Costa <glauber@scylladb.com>
After recent changes to the memtable code, there is no reason for us to
uphold a maximum memtable size. Now that we only flush one memtable at a
time anyway, and also have soft limit notifications from the
region_group_reclaimer, we can just set the soft limit to the target
size and let all of that be handled by the dirty_memory_manager.
It does have the added property that we'll be flushing when we globally
reach the soft limit threshold. In conditions in which we have multiple
CF writes fighting for memory, that guarantees that we will start
flushing much earlier than the hard limit.
The threshold is set to 1/4 of dirty memory. While in theory we would
prefer the memtables to go as big as 1/2 of dirty memory, in my
experiments I have found 1/4 to be a better fit, at least for the
moment.
The reason for such behavior is that in situations where we have slow
disks, setting the soft limit to 1/2 of dirty will put us in a situation
in which we may not have finished writing down the memtable when we hit
the limit, and then throttle. When set the threshold to 1/4 of dirty, we
don't throttle at all.
This behavior could potentially be fixed by not doing the full
memtable-based throttling after we do the commitlog throttling, but that
is not something realistic for the moment.
Signed-off-by: Glauber Costa <glauber@scylladb.com>
We would like to know from which region is a particular flush coming
from, and account accordingly. The reasoning behind that, is that soon
we'll be driving the flushes internally from the dirty_memory_manager
without explcitly triggering them.
We need to start a flush before the current one finishes, otherwise
we'll have a period without significant disk activity when the current
SSTable is being sealed, the caches are being updated, etc.
Signed-off-by: Glauber Costa <glauber@scylladb.com>
Right now we are calculating latencies only when we are about to add an
item to the memtable.
That's incorrect and misleading, for two reasons. First, it leaves the
commitlog latencies out. But second, it is done after the memtable wall
effect is applied, which means we are not counting throttle time neither
in the memtables or in the commitlog.
To do that, we'll start the latency_counter object as soon as possible
and move it all the way to apply_in_memory(). That should span the
entire write operation.
Signed-off-by: Glauber Costa <glauber@scylladb.com>
Message-Id: <4e424780d290fd5938046060df2b17e2b470b717.1478111467.git.glauber@scylladb.com>
There are places in which we need to use the column family object many
times, with deferring points in between. Because the column family may
have been destroyed in the deferring point, we need to go and find it
again.
If we use lw_shared_ptr, however, we'll be able to at least guarantee
that the object will be alive. Some users will still need to check, if
they want to guarantee that the column family wasn't removed. But others
that only need to make sure we don't access an invalid object will be
able to avoid the cost of re-finding it just fine.
Signed-off-by: Glauber Costa <glauber@scylladb.com>
Message-Id: <722bf49e158da77ff509372c2034e5707706e5bf.1478111467.git.glauber@scylladb.com>
Limiting the concurrency of memtable flushes to 4 was a temporary
workaround for the fact that we lacked good write behind support. Now
that write behind is properly merged we can reduce the concurrency to
what it should be, one.
This means that memtable flushes will now be serialized, and only when
one of them ends will the next one begin. Disk parallelism is obtained
through the write-behind mechanism.
Fixes#1373
Signed-off-by: Glauber Costa <glauber@scylladb.com>
Message-Id: <528f9ef928b5101bed952df600eb8555c275497a.1475881100.git.glauber@scylladb.com>
There is a limit to concurrency of sstable readers on each shard. When
this limit is exhausted (currently 100 readers) readers queue. There
is a timeout after which queued readers are failed, equal to
read_request_timeout_in_ms (5s by default). The reason we have the
timeout here is primarily because the readers created for the purpose
of serving a CQL request no longer need to execute after waiting
longer than read_request_timeout_in_ms. The coordinator no longer
waits for the result so there is no point in proceeding with the read.
This timeout should not apply for readers created for streaming. The
streaming client currently times out after 10 minutes, so we could
wait at least that long. Timing out sooner makes streaming unreliable,
which under high load may prevent streaming from completing.
The change sets no timeout for streaming readers at replica level,
similarly as we do for system tables readers.
Fixes#1741.
Message-Id: <1475840678-25606-1-git-send-email-tgrabiec@scylladb.com>
Currently, we export the region group where memtables are placed as dirty bytes.
Upcoming patches will optimistically mark some bytes in this region as free, a
scheme we know as "virtual dirty".
We are still interested in knowing the real state of the dirty region, so we
will keep track of the bytes virtually freed and split the counters in two.
Signed-off-by: Glauber Costa <glauber@scylladb.com>
The make_streaming_reader returns a combined mutation reader reads
mutations from sstables and memtable. The memtable reader handles
memtable flushing automatically so no special handling is needed here.
It will be used by streaming soon.
That's needed to observe behavior of clustering filter, and to
check if it's worthwhile for a specific workload.
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
This patch makes the optional trace_state_ptr arguments introduced in
previous patches mandatory where possible. Functions which are called
internally don't have a trace context, so for those we keep the
argument's default value for convenience.
Signed-off-by: Duarte Nunes <duarte@scylladb.com>
This patch changes the database and column_family types so a
trace_state_ptr can be passed in when querying. This enables tracing
of the inner components.
Signed-off-by: Duarte Nunes <duarte@scylladb.com>
The make_reader method is currently a const method, but we would like to start
keeping hit statistics from it.
Instead of relaxing the const condition too much, we can just mark the _stats
field as mutable, indicating that make_reader will not be able to change
anything in the CF, except for keeping statistics.
Signed-off-by: Glauber Costa <glauber@scylladb.com>
There is nothing really that fundamentally ties the estimated histogram to
sstables. This patch gets rid of the few incidental ties. They are:
- the namespace name, which is now moved to utils. Users inside sstables/
now need to add a namespace prefix, while the ones outside have to change
it to the right one
- sstables::merge, which has a very non-descriptive name to begin with, is
changed to a more descriptive name that can live inside utils/
- the disk_types.hh include has to be removed - but it had no reason to be
here in the first place.
Todo, is to actually move the file outside sstables/. That is done in a separate
step for clarity.
Signed-off-by: Glauber Costa <glauber@scylladb.com>
Remove clustering_key_filter_factory and clustering_key_filtering_context.
Use partition_slice directly with a static get_ranges method.
Signed-off-by: Piotr Jastrzebski <piotr@scylladb.com>
This patch adds an utility function that allows fetching the set of
column_families that do not belong to the system keyspace.
Signed-off-by: Duarte Nunes <duarte@scylladb.com>
This patch allows a set of a column_family's sstables to be
selected according to a range of ring_positions.
Signed-off-by: Duarte Nunes <duarte@scylladb.com>
memtable_list::seal_on_overlflow() is called on each mutation to check
if current memtable should be flushed. It will call
memtable_list::seal_active_memtable() when that is the case.
The number of concurrent seals is guarded by a semaphore, starting
from commit 0f64eb7e7d, and allows
at most 4 of them.
If there are 4 flushes already pending, every incoming mutation will
enqueue a new flush task on the semaphore's wait list, without waiting
for it. The wait queue can grow without bounds, eventually leading to
out-of-memory.
The fix is to seal the memtable immediately to satisfy should_flush()
condition, but limit concurrency of actual flushes. This way the wait
queue size on the semaphore is limited by memtables pending a flush,
which is fairly limited.
Message-Id: <1467997652-16513-1-git-send-email-tgrabiec@scylladb.com>
If mutations are fragmented during streaming a special care must be
taken so that isolation guarantees are not broken.
Mutations received with flag "fragmented" set are applied to a memtable
that is used only by that particular streaming task and the sstables
created by flushing such memtables are not made visible until the task
is complte. Also, in case the streaming fails all data is dropped.
This means that fragmented mutations cannot benefit from coalescing of
writes from multiple streaming plans, hence separate way of handling
them so that there is no loss of performance for small partitions.
Signed-off-by: Paweł Dziepak <pdziepak@scylladb.com>
plan_id is needed to keep track of the origin of mutations so that if
they are fragmented all fragments are made visible at the same time,
when that particular streaming plan_id completes.
Basically, each streaming plan that sends big (fragmented) mutations is
going to have its own memtables and a list of sstables which will get
flushed and made visible when that plan completes (or dropped if it
fails).
Signed-off-by: Paweł Dziepak <pdziepak@scylladb.com>
When flush_streaming_mutations() is called at the end of streaming it is
supposed to flush all data and then invalidate cache. ranges However, if
there are already some memtable flushes in progress it won't wait for them.
Signed-off-by: Paweł Dziepak <pdziepak@scylladb.com>
Issue 1195 describes a scenario with a fairly easy reproducer in which we can
freeze the database. That involves writing simultaneously to multiple CFs, such
that the sum of all the memory they are using is larger than the dirty memory
limit, without not any of them individually being larger than the memtable size.
Because we will never reach the individual memtable seal size for any of them,
none of them will initiate a flush leading the database to a halt.
The LSA has now gained infrastructure that allow us to be notified when pressure
conditions mount. What we will do in this case is initiate a flush ourselves.
Fixes#1195
Signed-off-by: Glauber Costa <glauber@scylladb.com>
In the spirit of what we are doing for the read semaphore, this patch moves
system writes to its own dirty memory manager. Not only will it make sure that
system tables will not be serialized by its own semaphore, but it will also put
system tables in its own region group.
Moving system tables to its own region group has the advantage that system
requests won't be waiting during throttle behind a potentially big queue of user
requests, since requests are tended to in FIFO order within the same region
group. However, system tables being more controlled and predictable, we can
actually go a step further and give them some extra reservation so they may not
necessarily block even if under pressure (up to 10 MB more).
Signed-off-by: Glauber Costa <glauber@scylladb.com>
We currently have a semaphore in the column family level that protects us against
multiple concurrent sstable flushes. However, storing that semaphore into the CF,
not the database, was a (implementation, not design) mistake.
One comment in particular makes it quite clear:
// Ideally, we'd allow one memtable flush per shard (or per database object), and write-behind
// would take care of the rest. But that still has issues, so we'll limit parallelism to some
// number (4), that we will hopefully reduce to 1 when write behind works.
So I aimed for the shard, but ended up coding it into the CF because that's closer to the
flush point - my bad.
This patch fixes this while paving the way for active reclaim to take place. It wraps the semaphore
and the region group in a new structure, the dirty_memory_manager. The immediate benefit is that we
don't need to be passing both the semaphore and the region group downwards in the DB -> CF path. The
long term benefit is that we now have a one unified structure that can hold shared flush data in all
of the CFs.
Signed-off-by: Glauber Costa <glauber@scylladb.com>
The LSA infrastructure, through the use of its region groups, now have
a throttler mechanism built-in. This patch converts the current throttlers
so that the LSA throttler is used instead.
Signed-off-by: Glauber Costa <glauber@scylladb.com>
