A seletion contains - in addition to the list of sstables - a next_token
which is a hint as to what is the next best token to call select() with.
This should be the smallest token such that at the next call to
select() the least number of new sstables will be returned, without
skipping any.
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>
so now user can look at nodetool compactionstats and determine
whether or not resharding is running, for example:
$ ./bin/nodetool compactionstats
pending tasks: 3
id compaction type keyspace table completed total unit progress
<none> RESHARD system compaction_history 11 256 keys 4.30%
<none> RESHARD system compaction_history 2 256 keys 0.78%
<none> RESHARD system compaction_history 10 256 keys 3.91%
<none> RESHARD system compaction_history 8 256 keys 3.12%
<none> RESHARD system compaction_history 7 256 keys 2.73%
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
Message-Id: <20170620175733.25882-1-raphaelsc@scylladb.com>
Currently, start and end size of compaction are calculated using the
uncompressed size of data component. bytes_on_disk() returns size
used by all components.
NOTE: start and end size are written to compaction history, so users
who monitor it should be aware of this change.
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
Message-Id: <20170525212129.6758-1-raphaelsc@scylladb.com>
- introcduced "seastarx.hh" header, which does a "using namespace seastar";
- 'net' namespace conflicts with seastar::net, renamed to 'netw'.
- 'transport' namespace conflicts with seastar::transport, renamed to
cql_transport.
- "logger" global variables now conflict with logger global type, renamed
to xlogger.
- other minor changes
After compaction revamp, compaction type set by cleanup at its ctor
is being overwritten at compaction::setup(). Consequently, cleanup
would not be stopped by 'nodetool stop cleanup' and cleanup would
be listed as regular compaction in 'nodetool compactionstats'.
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
Message-Id: <20170504013046.23522-1-raphaelsc@scylladb.com>
Some fields that belong to regular and cleanup aren't needed for
resharding_compaction, such as incremental selector (which is used
for determining max purgeable timestamp for a given decorated key)
Better move those fields to regular and make cleanup inherit from
regular compaction.
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
Message-Id: <20170428195611.9196-1-raphaelsc@scylladb.com>
Currently, fully expired sstable[1] is unconditionally chosen for compaction
by DTCS, but that may lead to a compaction loop under certain conditions.
Let's consider that an almost expired sstable is compacted, and it's not
deleted yet, and that the new sstable becomes expired before its ancestor is
deleted.
Because this new sstable is expired, it will be chosen by DTCS, but it will
not be purged because 'compacted undeleted' sstables are taken into account
by calculation of max purgeable timestamp and prevents expired data from
being purged. The problem is that this sequence of events can keep happening
forever as reported by issue #2260.
NOTE: This problem was easier to reproduce before improvement on compaction
of expired cells, because fully expired sstable was being converted into a
sstable full of tombstones, which is also considered fully expired.
Fixes#2260.
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
Message-Id: <20170428233554.13744-1-raphaelsc@scylladb.com>
This patch replaces the current row tombstone representation by a
row_tombstone.
The intent of the patch is thus to reify the idea of shadowable
tombstones, that up until now we considered all materialized view row
tombstones to be.
We need to distinguish shadowable from non-shadowable row tombstones
to support scenarios such as, when inserting to a table with a
materialzied view:
1. insert into base (p, v1, v2) values (3, 1, 3) using timestamp 1
2. delete from base using timestamp 2 where p = 3
3. insert into base (p, v1) values (3, 1) using timestamp 3
These should yield a view row where v2 is definitely null, but with
the current implementation, v2 will pop back with its value v2=3@TS=1,
even though its dead in the base row. This is because the row
tombstone inserted at 2) is a shadowable one.
This patch only addresses the memory representation of such
row_tombstones.
Signed-off-by: Duarte Nunes <duarte@scylladb.com>
Extends compaction for new resharding algorithm. Not wired yet.
New resharding will compact shared sstable(s) and create one
sstable for each owner. It's up to the caller to open these
new unshared sstables at their respective column families.
This new approach will save a lot of bandwidth because we'll
no longer read the entire shared sstable #smp::count times.
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
compacting_sstable_writer only allowed one writer so far, but we will need
multiple ones for resharding.
It's done by moving writer management to compaction.
finish_sstable_writer() is added for compaction impl to stop all writers,
whereas stop_sstable_writer() will only stop current writer (needed when
current sstable reaches max limit size for example).
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
No need for compacting_sstable_writer to store items that are available
in compaction class. Also, that's a step towards supporting multiple
writers for compaction.
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
compact_sstables() supported both regular and cleanup compaction,
but with lots of conditions that made it ugly and hard to extend.
In the future, we want to introduce a new type of compaction for
resharding that will create one sstable for every shard owning
the sstable(s) given as input. That will be easier now.
Reviewed-by: Nadav Har'El <nyh@scylladb.com>
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
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>
Wrapping ranges are a pain, so we are moving wrap handling to the edges.
Since cql can't generate wrapping ranges, this means thrift and the ring
maintenance code; also range->ring transformations need to merge the first
and last ranges.
Message-Id: <1478105905-31613-1-git-send-email-avi@scylladb.com>
Originally, streamed_mutations guaranteed that emitted tombstones are
disjoint. In order to achieve that two separate objects were produced
for each range tombstone: range_tombstone_begin and range_tombstone_end.
Unfortunately, this forced sstable writer to accumulate all clustering
rows between range_tombstone_begin and range_tombstone_end.
However, since there is no need to write disjoint tombstones to sstables
(see #1153 "Write range tombstones to sstables like Cassandra does") it
is also not necessary for streamed_mutations to produce disjoint range
tombstones.
This patch changes that by making streamed_mutation produce
range_tombstone objects directly.
Signed-off-by: Paweł Dziepak <pdziepak@scylladb.com>
Checking bloom filters of sstables to compute max purgeable timestamp
for compaction is expensive in terms of CPU time. We can avoid
calculating it if we're not about to GC any tombstone.
This patch changes compacting functions to accept a function instead
of ready value for max_purgeable.
I verified that bloom filter operations no longer appear on flame
graphs during compaction-heavy workload (without tombstones).
Refs #1322.
2a46410f4a changed sstable_list from a map
to a set, so it is no longer sorted by generation. The code for finding
the list of sstables not being compacted relied on this sort order, and
now broke, returning a longer list than needed (including some of the
sstables being compacted). As a result, the compaction code preserved
the tombstones, incorrectly thinking there was still live data they
referenced.
Fix by sorting the set explicitly.
Fixes#1429.
Message-Id: <1467793026-6571-1-git-send-email-avi@scylladb.com>
Strongly based on org.apache.cassandra.db.compaction.
CompactionController.getFullyExpiredSSTables.
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
In a leveled column family, there can be many thousands of sstables, since
each sstable is limited to a relatively small size (160M by default).
With the current approach of reading from all sstables in parallel, cpu
quickly becomes a bottleneck as we need to check the bloom filter for each
of these sstables.
This patch addresses the problem by introducing a
compaction-strategy-specific data structure for holding sstables. This
data structure has a method to obtain the sstables used for a read.
For leveled compaction strategy, this data structure is an interval map,
which can be efficiently used to select the right sstables.
sstable_list is now a map<generation, sstable>; change it to a set
in preparation for replacing it with sstable_set. The change simplifies
a lot of code; the only casualty is the code that computes the highest
generation number.
This patch moves compaction logic to a consumer that can be used with
consume_flattened_in_thread(). Internally, sstable_writer is used to
write individual sstables.
Signed-off-by: Paweł Dziepak <pdziepak@scylladb.com>
Currently, each sstable write has its separate thread. However, the goal
is to have compaction use consume_flattened() with a consumer that
creates and writes the sstables. consume_flattened() needs to be executed
inside a thread, since sstable writer may defer.
This patch is a first step in preparations and it just makes whole
compaction logic run inside a thread. That makes little sense now, since
all sstable writes spawn their own threads but that's going to change
in the following patches.
Signed-off-by: Paweł Dziepak <pdziepak@scylladb.com>
"If we compact sstables A, B into a new sstable C we must either delete both
A and B, or none of them. This is because a tombstone in B may delete data
in A, and during compaction, both the tombstone and the data are removed.
If only B is deleted, then the data gets resurrected.
Non-atomic deletion occurs because the filesystem does not support atomic
deletion of multiple files; but the window for that is small and is not
addressed in this patchset. Another case is when A is shared across
multiple shards (as is the case when changing shard count, or migrating
from existing Cassandra sstables). This case is covered by this patchset.
Fixes #1181."
If sstables A, B are compacted, A and B must be deleted atomically.
Otherwise, if A has data that is covered by a tombstone in B, and that
tombstone is deleted, and if B is deleted while A is not, then the data
in A is resurrected.
Fixes#1181.
This change will allow user to specify the maximum size of a new sstable
created as a result of leveled compaction.
Example of using this setting:
ALTER TABLE ks.test5 with compaction = {'sstable_size_in_mb': '1000',
'class': 'LeveledCompactionStrategy'}
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
Message-Id: <ebb9844401af74388bda12586c2435283f6d8db8.1460486043.git.raphaelsc@scylladb.com>
When we, for some reason, fail to compact an SSTable, we do not log the file
name leaving us with cryptic messages that tell us what happened, but not where
it happened.
This patch adds logging in compaction so that we'll know what's going on.
Please note that readers are more of a concern, because the SSTable being
written technically do not exist yet. Still, better safe than sorry: if
open_data fails, or we leave an unfinished SSTable, it is still good to know
which one was the culprit.
Some argument can be made about whether we should log this at the lower SSTable
level, or at the compaction level.
The reason I am logging this at the compaction level, is that we don't really
know which exception will trigger, and where: it may be the case that we're
seeing exceptions that are not SSTable specific, and may not have the chance to
log it properly.
In particular, if the exception happens inside the reader: read_rows() and
friends only return a mutation reader, which doesn't really do anything until
we call read(). But at that time, we don't hold any pointers to the SSTable
anymore.
In Summary, logging at the compaction level guarantees that we always do it no
matter what. Exceptions that are part of the main SSTable path can log the file
name as well if they want: if that's the case, we'll be left with the name
appearing twice. That's totally harmless, and better than none.
Fixes#1123
Signed-off-by: Glauber Costa <glauber@scylladb.com>
Message-Id: <c5c969fb6aeb788a037bd7a4ea69979c1042cb34.1459263847.git.glauber@scylladb.com>
When scylla stopped an ongoing compaction, the event was reported
as an error. This patch introduces a specialized exception for
compaction stop so that the event can be handled appropriately.
Before:
ERROR [shard 0] compaction_manager - compaction failed: read exception:
std::runtime_error (Compaction for keyspace1/standard1 was deliberately
stopped.)
After:
INFO [shard 0] compaction_manager - compaction info: Compaction for
keyspace1/standard1 was stopped due to shutdown.
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
Message-Id: <1f85d4e5c24d23a1b4e7e0370a2cffc97cbc6d44.1455034236.git.raphaelsc@scylladb.com>
storage_service::get_local_ranges returns sorted ranges, which are
not overlapping nor wrap-around. As a result, there is no need for
the consumer to do anything.
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
After this patch, our I/O operations will be tagged into a specific priority class.
The available classes are 5, and were defined in the previous patch:
1) memtable flush
2) commitlog writes
3) streaming mutation
4) SSTable compaction
5) CQL query
Signed-off-by: Glauber Costa <glauber@scylladb.com>
"This series moves the "backup" logic into the sstable::write_components()
methods, adds a support for enabling backup for sstables flushed in the
compaction flow (in addition to a regular flushing flow which had this support
already) and enables the "incremental_backups" configuration option."
I fixed up a merge conflict with commit 5e953b5 ("Merge "Add support to
stop ongoing compaction" from Raphael").
