Previously, the disk block alignment of segments was hardcoded (due to
really old code). Now we use the value as declared in the actual file
opened. If we are using a previously written file (i.e. o_dsync), we
can even use the sometimes smaller "read" alignment.
Also allow config to completely override this with a disk alignment
config option (not exposed to global config yet, but can be).
v2:
* Use overwrite alignment if doing only overwrite
* Ensure to adjust actual alignment if/when doing file wrapping
v3:
* Kill alignment config param. Useless and unsafe.
Closes#8935
Commitlog timer issues un-waited syncs on all segments. If such
a sync takes too long we can end up keeping a segment alive across
a shutdown, causing the file to be left on disk, even if actually
clean.
This adds a future in segment_manager that is "chained" with all
active syncs (hopefully just one), and ensures we wait for this
to complete in shutdown, before pruning and deleting segments
In case we only have a single segment active when shutting down,
the replenisher can be blocked even though we manually flush-deleted.
Add a signal type and abort queues using this to wake up waiter and
force them to check shutdown status.
If we are using recycling, we should always use recycle in
delete_segments, otherwise we can cause deadlock with replenish
task, since it will be waiting for segment, then shutdown is set,
and we are called, and can't fulfil the alloc -> deadlock
If a segments, when finishing a flush call, is deletable, we should issue
a manual call to discard function (which moves deleteable segments off
segment list) asap, since we otherwise are dependent on more calls
from flush handlers (memtable flush). And since we could have blocked
segment allocation, this can cause deadlocks, at least in tests.
Refs #8270
Since segment allocation looks at actual disk footprint, not active,
the threshold check in timer task should include slack space so we
don't mistake sparse usage for space left.
Refs #8270
Try to ensure we issue a flush as soon as we are allocating in the
last allowable segment, instead of "half through". This will make
flushing a little more eager, but should reduce latencies created
by waiting for segment delete/recycle on heavy usage.
Currently, if sync_all_segments fails during shutdown,
_shutdown is never set, causing replenish_reserve
to hang, as possibly seen in #8577.
It is better if scylla aborts on critical errors
during shutdown rather than just hang.
Refs #8577
Test: unit(dev)
DTest: commitlog_test.py
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
This was triggered by the test_total_space_limit_of_commitlog dtest.
When it passes a very large commitlog_segment_size_in_mb (1/6th of the
free memory size, in mb), segment_manager constructor limits max_size
to std::numeric_limits<position_type>::max() which is 0xffffffff.
This causes allocate_segment_ex to loop forever when writing the segment
file since `dma_write` returns 0 when the count is unaligned (seen 4095).
The fix here is to select a sligtly small maxsize that is aligned
down to a multiple of 1MB.
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
Message-Id: <20210407121059.277912-1-bhalevy@scylladb.com>
Fixes#8376
If a recycle should fail, we will sort of handle it by deleting
the segment, so no leaks. But if we have waiter(s) on the recycle
queue, we could end up deadlocked/starved because nothing is
incoming there.
This adds an abort of the queue iff we failed and no objects are
available. This will wake up any waiter, and he should retry,
and hopefully at least be able to create a new segment.
We then reset the queue to a new one. So we can go on.
v2:
* Forgot to reset queue
v3:
* Nicer exception handling in allocate_segment_ex
Fixes#8363
Delete segements has two issues when running with size-limited
commit log and strict adherence to said limit.
1.) It uses parallel processing, with deferral. This means that
the disk usage variables it looks at might not be fully valid
- i.e. we might have already issued a file delete that will
reduce disk footprint such that a segment could instead be
recycled, but since vars are (and should) only updated
_post_ delete, we don't know.
2.) It does not take into account edge conditions, when we only
delete a single segment, and this segment is the border segment
- i.e. the one pushing us over the limit, yet allocation is
desperately waiting for recycling. In this case we should
allow it to live on, and assume that next delete will reduce
footprint. Note: to ensure exact size limit, make sure
total size is a multiple of segment size.
Fixed by
a.) Doing delete serialized. It is not like being parallel here will
win us speed awards. And now we can know exact footprint, and
how many segments we have left to delete
b.) Check if we are a block across the footprint boundry, and people
might be waiting for a segment. If so, don't delete segment, but
recycle.
As a follow-up, we should probably instead adjust the commitlog size
limit (per shard) to be a multiple of segment sizes, but there is
risks in that too.
Fixes#8369
This was originally found (and fixed) by @gleb-cloudius, but the patch set with
the fix was reverted at some point, and the fix went away. Now the error remains
even in new, nice coroutine code.
We check the wrong var in the inner loop of the pre-fill path of
allocate_segment_ex, often causing us to generate giant writev:s of more or less
the whole file. Not intended.
Closes#8370
This open option tells seastar that the file in question
will be truncated to the needed size right at once and all
the subsequent writes will happen within this size. This
hint turns off append optimization in seastar that's not
that cheap and helps so save few cpu cycles.
The option was introduced in seastar by 8bec57bc.
tests: unit(dev), dtest(commitlog:
test_batch_commitlog,
test_periodic_commitlog,
test_commitlog_replay_on_startup)
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
Message-Id: <20210323115409.31215-1-xemul@scylladb.com>
Refs #7794
Iff we need to pre-fill segment file ni O_DSYNC mode, we should
drop this for the pre-fill, to avoid issuing flushes until the file
is filled. Done by temporarily closing, re-opening in "normal" mode,
filling, then re-opening.
v2:
* More comment
v3:
* Add missing flush
v4:
* comment
v5:
* Split coroutine and fix into separate patches
This commit adds an option which, when turned on, allows the commitlog
to go over configured size limit. After reaching the limit, commitlog
will be more conservative with its usage of the disk space - for
example, it won't increase the segment reserve size or reuse recycled
segments. Most importantly, it won't block writes until the space used
by the commitlog goes down.
This change is necessary for hinted handoff to keep its current
behavior. Hinted handoff does not let the commitlog free segments
itself - instead, it re-creates it every 10 seconds and manually deletes
segments after all hints are sent from a segment.
Commit aab6b0ee27 introduced the
controversial new IMR format, which relied on a very template-heavy
infrastructure to generate serialization and deserialization code via
template meta-programming. The promise was that this new format, beyond
solving the problems the previous open-coded representation had (working
on linearized buffers), will speed up migrating other components to this
IMR format, as the IMR infrastructure reduces code bloat, makes the code
more readable via declarative type descriptions as well as safer.
However, the results were almost the opposite. The template
meta-programming used by the IMR infrastructure proved very hard to
understand. Developers don't want to read or modify it. Maintainers
don't want to see it being used anywhere else. In short, nobody wants to
touch it.
This commit does a conceptual revert of
aab6b0ee27. A verbatim revert is not
possible because related code evolved a lot since the merge. Also, going
back to the previous code would mean we regress as we'd revert the move
to fragmented buffers. So this revert is only conceptual, it changes the
underlying infrastructure back to the previous open-coded one, but keeps
the fragmented buffers, as well as the interface of the related
components (to the extent possible).
Fixes: #5578
Refs #6148
Commitlog disk limit was previously a "soft" limit, in that we allowed allocating new segments, even if we were over
disk usage max. This would also cause us sometimes to create new segments and delete old ones, if badly timed in
needing and releasing segments, in turn causing useless disk IO for pre-allocation/zeroing.
This patch set does:
* Make limit a hard limit. If we have disk usage > max, we wait for delete or recycle.
* Make flush threshold configurable. Default is ask for flush when over 50% usage. (We do not wait for results)
* Make flush "partial". We flush X% of the used space (used - thres/2), and make the rp limit accordingly. This means we will try to clear the N oldest segments, not all. I.e. "lighter" flush. Of course, if the CL is wholly dominated by a single CF, this will not really help much. But when > 1 cf is used, it means we can skip those not having unflushed data < req rp.
* Force more eager flush/recycle if we're out of segments
Note: flush threshold is not exposed in scylla config (yet). Because I am unsure of wording, and even if it should.
Note: testing is sparse, esp. in regard to latency/timeouts added in high usage scenarios. While I can fairly easily provoke "stalls" (i.e. forced waiting for segments to free up) with simple C-S, it is hard to say exactly where in a more sane config (I set my limits looow) latencies will start accumulating.
Closes#7879
* github.com:scylladb/scylla:
commitlog: Force earlier cycle/flush iff segment reserve is empty
commitlog: Make segment allocation wait iff disk usage > max
commitlog: Do partial (memtable) flushing based on threshold
commitlog: Make flush threshold configurable
table: Add a flush RP mark to table, and shortcut if not above
Fixes#7615
Allows N mutations to be written "atomically" (i.e. in the same
call). Either all are added to segement, or none.
Returns rp_handle vector corresponding to the call vector.
Allows writing more than one blob of data using a single
"add" call into segment. The old call sites will still
just provide a single entry.
To ensure we can determine the health of all the entries
as a unit, we need to wrap them in a "parent" entry.
For this, we bump the commitlog segment format and
introduce a magic marker, which if present, means
we have entries in entry, totalling "size" bytes.
We checksum the entra header, and also checksum
the individual checksums of each sub-entry (faster).
This is added as a post-word.
When parsing/replaying, if v2+ and marker, we have to
read all entries + checksums into memory, verify, and
_then_ we can actually send the info to caller.
This reverts commit df2f67626b. The fix
is correct, but has an unfortunate side effect with O_DSYNC: each
128k write also needs to flush the XFS log. This translates to
32MB/128k = 256 flushes, compared to one flush with the original code.
A better fix would be to prezero without O_DSYNC, then reopen the file
with O_DSYNC, but we can do that later.
Reopens#5857.
Attempt to hurry flushing/segment delete/recycle if we are trying
to get a segment for allocation, and reserve is empty when above
disk threshold. This is minimize time waited in allocation semaphore.
When recycling a segment in O_DSYNC mode if the size of the segment
is neither shrunk nor grown, avoid calling file::truncate() or
file::allocate().
Message-Id: <20201215182332.1017339-2-kostja@scylladb.com>
Normally a file size should be aligned around block size, since
we never write to it any unaligned size. However, we're not
protected against partial writes.
Just to be safe, align up the amount of bytes to zerofill
when recycling a segment.
Message-Id: <20201211142628.608269-4-kostja@scylladb.com>
C++20 introduced `contains` member functions for maps and sets for
checking whether an element is present in the collection. Previously
`count` function was often used in various ways.
`contains` does not only express the intend of the code better but also
does it in more unified way.
This commit replaces all the occurences of the `count` with the
`contains`.
Tests: unit(dev)
Signed-off-by: Piotr Jastrzebski <piotr@scylladb.com>
Message-Id: <b4ef3b4bc24f49abe04a2aba0ddd946009c9fcb2.1597314640.git.piotr@scylladb.com>
Refs #6148
Separates disk usage into two cases: Allocated and used.
Since we use both reserve and recycled segments, both
which are not actually filled with anything at the point
of waiting.
Also refuses to recycle segments or increase reserve size
if our current disk footprint exceeds threshold.
And finally uses some initial heuristics to determine when
we should suggest flushing, based on disk limit, segment
size, and current usage. Right now, when we only have
a half segment left before hitting used == max.
Some initial tests show an improved adherence to limit
though it will still be exceeded, because we do _not_
force waiting for segments to become cleared or similar
if we need to add data, thus slow flushing can still make
usage create extra segments. We will however attempt to
shrink disk usage when load is lighter.
Somewhat unclear how much this impacts performance
with tight limits, and how much this matters.
v2:
* Add some comments/explanations
v3:
* Made disk footprint subtract happen post delete (non-optimistic)
C++20 introduced std::erase_if which simplifies removal of elements
from the collection. Previously the code pattern looked like:
<collection>.erase(
std::remove_if(<collection>.begin(), <collection>.end(), <predicate>),
<collection>.end());
In C++20 the same can be expressed with:
std::erase_if(<collection>, <predicate>);
This commit replaces all the occurences of the old pattern with the new
approach.
Tests: unit(dev)
Signed-off-by: Piotr Jastrzebski <piotr@scylladb.com>
Message-Id: <6ffcace5cce79793ca6bd65c61dc86e6297233fd.1597064990.git.piotr@scylladb.com>
Besdies being more robust than passing const descriptor&
to continuations, this helps simplify making allocate_segment_ex's
continuations nothrow_move_constructible, that is need for using
seastar::with_file_close_on_failure().
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
When a mutation is written to the commitlog, a rp_handle object is
returned which keeps a reference to commitlog segment. A segment is
"dirty" when its reference count is not zero, otherwise it is "clean".
When commitlog object is being destroyed, a warning is being printed
for every dirty segment. On the other hand, clean segments are deleted.
In case of standard mutation writing path, the rp_handle moves
responsibility for releasing the reference to the memtable to which the
mutation is written. When the memtable is flushed to disk, all
references accumulated in the memtable are released. In this context, it
makes sense to warn about dirty segments, because such segments contain
mutations that are not written to sstables, and need to be replayed.
However, hinted handoff uses a different workflow - it recreates a
commitlog object periodically. When a hint is written to commitlog, the
rp_handle reference is not released, so that segments with hints are not
deleted when destroying the commitlog. When commitlog is created again,
we get a list of saved segments with hints that we can try to send at a
later time.
Although this is intended behavior, now that releasing the hints
commitlog is done properly, it causes the mentioned warning to
periodically appear in the logs.
This patch adds a parameter for the commitlog that allows to disable
this warning. It is only used when creating hinted handoff commitlogs.
This makes the code a bit easier to read as there are no discarded
futures and no references to having to keep a subscription alive,
which we don't with current seastar.
Signed-off-by: Rafael Ávila de Espíndola <espindola@scylladb.com>
Message-Id: <20200527013120.179763-1-espindola@scylladb.com>
Seastar recently lost support for the experimental Concepts Technical
Specification (TS) and gained support for C++20 concepts. Re-enable
concepts in Scylla by updating our use of concepts to the C++20
standard.
This change:
- peels off uses of the GCC6_CONCEPT macro
- removes inclusions of <seastar/gcc6-concepts.hh>
- replaces function-style concepts (no longer supported) with
equation-style concepts
- semicolons added and removed as needed
- deprecated std::is_pod replaced by recommended replacement
- updates return type constraints to use concepts instead of
type names (either std::same_as or std::convertible_to, with
std::same_as chosen when possible)
No attempt is made to improve the concepts; this is a specification
update only.
Message-Id: <20200531110254.2555854-1-avi@scylladb.com>
C++20 deprecates capturing this in default-copy lambdas ([=]), with
good reason. Move to explicit captures to avoid any ambiguity and
reduce warning spew.
Message-Id: <20200517150834.753463-1-avi@scylladb.com>
