'"The issue is triggered by compaction of sstables of level higher than 0.
The problem happens when interval map of partitioned sstable set stores
intervals such as follow:
[-9223362900961284625 : -3695961740249769322 ]
(-3695961740249769322 : -3695961103022958562 ]
When selector is called for first interval above, the exclusive lower
bound of the second interval is returned as next token, but the
inclusivess info is not returned.
So reader_selector was returning that there *were* new readers when
the current token was -3695961740249769322 because it was stored in
selector position field as inclusive, but it's actually exclusive.
This false positive was leading to infinite recursion in combined
reader because sstable set's incremental selector itself knew that
there were actually *no* new readers, and therefore *no* progress
could be made."
Fixes #2908.'
* 'high_level_compaction_infinite_recursion_fix_v4' of github.com:raphaelsc/scylla:
tests: test for infinite recursion bug when doing high-level compaction
Fix potential infinite recursion when combining mutations for leveled compaction
dht: make it easier to create ring_position_view from token
dht: introduce is_min/max for ring_position
(cherry picked from commit 375ed938b4)
"While aa8c2cbc16 'Merge "Migrate sstables
to flat_mutation_reader" from Piotr' has converted the low-level sstable
reader to the new flat_mutation_reader interface there were still
multiple readers related to sstables that required converting,
including:
- restricted reader
- filtering reader
- single partition sstable reader
This series completes their conversion to the flat stream interface."
* tag 'flat_mutation_reader-sstable-readers/v2' of https://github.com/pdziepak/scylla:
db: convert single_key_sstalbe_reader to flat streams
db: fully convert incremental_reader_selector to flat readers
db: make make_range_sstable_reader() return flat reader
db: make column_family::make_reader() return flat reader
db: make column_family::make_sstable_reader() return a flat reader
filtering_reader: switch to flat mutation fragment streams
filtering_reader: pass a const dht::decorated_key& to the callback
mutation_reader: drop make_restricted_reader()
db: use make_restricted_flat_reader
mutation_reader: convert restricted reader to flat streams
(cherry picked from commit 6cb3b29168)
When fast forwarding is enabled and all readers positioned inside the
current partition return EOS, return EOS from the combined-reader
too. Instead of skipping to the next partition if there are idle readers
(positioned at some later partition) available. This will cause rows to
be skipped in some cases.
The fix is to distinguish EOS'd readers that are only halted (waiting
for a fast-forward) from thoose really out of data. To achieve this we
track the last fragment-kind the reader emitted. If that was a
partition-end then the reader is out of data, otherwise it might emit
more fragments after a fast-forward. Without this additional information
it is impossible to determine why a reader reached EOS and the code
later may make the wrong decision about whether the combined-reader as
a whole is at EOS or not.
Also when fast-forwarding between partition-ranges or calling
next_partition() we set the last fragment-kind of forwarded readers
because they should emit a partition-start, otherwise they are out of
data.
Signed-off-by: Botond Dénes <bdenes@scylladb.com>
Message-Id: <6f0b21b1ec62e1197de6b46510d5508cdb4a6977.1512569218.git.bdenes@scylladb.com>
(cherry picked from commit 9661769313)
"Convert combined_mutation_reader into a flat_mutation_reader impl. For
now - in the name of incremental progress - all consumers are updated to
use the combined reader through the
mutation_reader_from_flat_mutation_reader adaptor. The combined reader also
uses all it's sub mutation_readers through the
flat_mutation_reader_from_mutation_reader adaptor."
* 'bdenes/flatten-combined-reader-v8' of https://github.com/denesb/scylla:
Add unit tests for the combined reader - selector interactions
Add flat_mutation_reader overload of make_combined_reader
Flatten the implementation of combined_mutation_reader
Add mutation_fragment_merger
mutation_fragment::apply(): handle partition start and end too
Add non-const overload of partition_start::partition_tombstone()
Make combined_mutation_reader a flat_mutation_reader
Move the mutation merging logic to combined_mutation_reader
Remove the unnecessary indirection of mutation_reader_merger::next()
Move the implementation of combined_mutation_reader into mutation_reader_merger
Remove unused mutation_and_reader::less_compare and operator<
(cherry picked from commit 046991b0b7)
Introduce sstable::read_row_flat and sstable::read_range_rows_flat methods
and use them in sstable::as_mutation_source.
* https://github.com/scylladb/seastar-dev/tree/haaawk/flat_reader_sstables_v3:
Introduce conversion from flat_mutation_reader to streamed_mutation
Add sstables::read_rows_flat and sstables::read_range_rows_flat
Turn sstable_mutation_reader into a flat_mutation_reader
sstable: add getter for filter_tracker
Move mp_row_consumer methods implementations to the bottom
Remove unused sstable_mutation_reader constructor
Replace "sm" with "partition" in get_next_sm and on_sm_finished
Move advance_to_upper_bound above sstable_mutation_reader
Store sstable_mutation_reader pointer in mp_row_consumer
Stop using streamed_mutation in consumer and reader
Stop using streamed_mutation in sstable_data_source
Delete sstable_streamed_mutation
Introduce sstable::read_row_flat
Migrate sstable::as_mutation_source to flat_mutation_reader
Remove single_partition_reader_adaptor
Merge data_consume_context::impl into data_consume_context
Create data_consume_context_opt.
Merge on_partition_finished into mark_partition_finished
Check _partition_finished instead of _current_partition_key
Merge sstable_data_source into sstable_mutation_reader
Remove sstable_data_source
Remove get_next_partition and partition_header
(cherry picked from commit aa8c2cbc16)
"This changeset is the first step to flatten mutation_reader.
Then it introduces new mutation_fragment types for partition header and end of partition.
Using those a new flat_mutation_reader is defined.
Finally it introduces converters between new flat_mutation_reader and
old mutation_reader."
* 'haaawk/flattened_mutation_reader_v12' of github.com:scylladb/seastar-dev:
Add tests for flat_mutation_reader
Introduce conversion from flat_mutation_reader to mutation_reader
Introduce conversion from mutation_reader to flat_mutation_reader
Introduce flat_mutation_reader
Extract FlattenedConsumer concept using GCC6_CONCEPT
Introduce partition_end mutation_fragment
Introduce a position for end of partition
Introduce partition_start mutation_fragment
Introduce FragmentConsumer
Introduce a position for partition start
streamed_mutation: Extract concepts using GCC6_CONCEPT macro
Update description of existing reader count metrics, add memory
consumption metrics. Use labels to distinguish between system, user and
streaming reads related metrics.
Restrict readers based on their memory consumption, instead of the count
of the top-level readers. To do this an interposer is installed at the
input_stream level which tracks buffers emmited by the stream. This way
we can have an accurate picture of the readers' actual memory
consumption.
New readers will consume 16k units from the semaphore up-front. This is
to account their own memory-consumption, apart from the buffers they
will allocate. Creating the reader will be deferred to when there are
enough resources to create it. As before only new readers will be
blocked on an exhausted semaphore, existing readers can continue to
work.
Restrict readers based on their memory consumption, instead of the count
of the top-level readers. To do this an interposer is installed at the
input_stream level which tracks buffers emmited by the stream. This way
we can have an accurate picture of the readers' actual memory
consumption.
New readers will consume 16k units from the semaphore up-front. This is
to account their own memory-consumption, apart from the buffers they
will allocate. Creating the reader will be deferred to when there are
enough resources to create it. As before only new readers will be
blocked on an exhausted semaphore, existing readers can continue to
work.
Exhausted readers can be fast forwarded, so we have to keep them
around. However, if the current reader is not fast forwardable, then
we can drop those readers and their buffers.
Signed-off-by: Duarte Nunes <duarte@scylladb.com>
combined_mutation_reader now accepts as a constructor argument a
reader_selector instance whoose task is to create new readers on
each call to operator()() if needed and possible.
This way it is possible to control how readers are created through
different specializations of reader_selector.
The previous logic is refactored into list_reader_selector which
is using a pre-provided mutation_reader list and forwards all of them to
combined_mutation_reader at once.
Since the discovery of std::exchange(x, {}) move_and_clear has become
obsolete. Beside, the name was wrong, it did not clear the vector but
recreated it meaning that any allocated memory wasn't reused (not that
it mattered in the existing usages).
Message-Id: <20170731123549.10887-1-pdziepak@scylladb.com>
Merging mutations is quite an expensive operation. The creation of
streamed mutation merger involves several allocations (mostly coming
from various std::vector) and then all mutation_fragments need to go
through a heap.
All this is completely unnecessary if there is only one mutation, so
let's skip a call to merge_mutations() in such cases. This also means
that we can reuse memory allocated by _current vector if merge is not
required.
Originally, the loop insidecombined_mutation_reader::next() so that it
was popping mutation from the heap and when it encountered one with a
different decorated key it was pushed back and the ones accumulated so
far merged and emitted. In other words, every time the reader progressed
to the next mutation it did needless pop and push operations on the
heap.
This patch rearranges the code so that the key of the next mutation is
compared before it is popped from the heap.
By default make_reader_returning creates a reader that does not
support fast forwarding but the second parameter can be used to
make it support fast forwarding.
[tgrabiec: Improve title]
Signed-off-by: Piotr Jastrzebski <piotr@scylladb.com>
multi_range_mutation_reader uses fast_forward_to() to skip between
ranges, so we always need to create the underlying reader with with
mutation_reader::forwarding::yes if there is more than one range,
irrespective of whether multi_range_mutation_reader itself will be
forwarded or not.
Fixes#2510.
Introduced in commit 3018df1.
Message-Id: <1497943032-18696-1-git-send-email-tgrabiec@scylladb.com>
In commit c63e88d556, support was added for
fast_forward_to() in data_consume_rows(). Because an input stream's end
cannot be changed after creation, that patch ignores the specified end
byte, and uses the end of file as the end position of the stream.
As result of this, even when we want to read a specific byte range (e.g.,
in the repair code to checksum the partitions in a given range), the code
reads an entire 128K buffer around the end byte, or significantly more, with
read-ahead enabled. This causes repair to do more than 10 times the amount
of I/O it really has to do in the checksumming phase (which in the current
implementation, reads small ranges of partitions at a time).
This patch has two levels:
1. In the lower level, sstable::data_consume_rows(), which reads all
partitions in a given disk byte range, now gets another byte position,
"last_end". That can be the range's end, the end of the file, or anything
in between the two. It opens the disk stream until last_end, which means
1. we will never read-ahead beyond last_end, and 2. fast_fordward_to() is
not allowed beyond last_end.
2. In the upper level, we add to the various layers of sstable readers,
mutation readers, etc., a boolean flag mutation_reader::forwarding, which
says whether fast_forward_to() is allowed on the stream of mutations to
move the stream to a different partition range.
Note that this flag is separate from the existing boolean flag
streamed_mutation::fowarding - that one talks about skipping inside a
single partition, while the flag we are adding is about switching the
partition range being read. Most of the functions that previously
accepted streamed_mutation::forwarding now accept *also* the option
mutation_reader::forwarding. The exception are functions which are known
to read only a single partition, and not support fast_forward_to() a
different partition range.
We note that if mutation_reader::forwarding::no is requested, and
fast_forward_to() is forbidden, there is no point in reading anything
beyond the range's end, so data_consume_rows() is called with last_end as
the range's end. But if forwarding::yes is requested, we use the end of the
file as last_end, exactly like the code before this patch did.
Importantly, we note that the repair's partition reading code,
column_family::make_streaming_reader, uses mutation_reader::forwarding::no,
while the other existing reading code will use the default forwarding::yes.
In the future, we can further optimize the amount of bytes read from disk
by replacing forwarding::yes by an actual last partition that may ever be
read, and use its byte position as the last_end passed to data_consume_rows.
But we don't do this yet, and it's not a regression from the existing code,
which also opened the file input stream until the end of the file, and not
until the end of the range query. Moreover, such an improvement will not
improve of anything if the overall range is always very large, in which
case not over-reading at its end will not improve performance.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20170619152629.11703-1-nyh@scylladb.com>
This reverts commit 317d7fc253 (and also the
related 2c57ab84b2). It causes crashes
during range scans, reported by Gleb:
"To reproduce I run SELECT * FROM keyspace1.standard1; on typical c-s
dataset and 3 node cluster.
Backtrace:
at /home/gleb/work/seastar/seastar/core/apply.hh:36
rvalue=<unknown type in /home/gleb/work/seastar/build/release/scylla, CU 0x54cf307, DIE 0x55ebf2a>) at /home/gleb/work/seastar/seastar/core/do_with.hh:57
range=std::vector of length 6, capacity 8 = {...}) at /home/gleb/work/seastar/seastar/core/future-util.hh:142
at ./seastar/core/future.hh:890
at /home/gleb/work/seastar/seastar/core/future-util.hh:119
at /home/gleb/work/seastar/seastar/core/future-util.hh:142
In commit c63e88d556, support was added for
fast_forward_to() in data_consume_rows(). Because an input stream's end
cannot be changed after creation, that patch ignores the specified end
byte, and uses the end of file as the end position of the stream.
As result of this, even when we want to read a specific byte range (e.g.,
in the repair code to checksum the partitions in a given range), the code
reads an entire 128K buffer around the end byte, or significantly more, with
read-ahead enabled. This causes repair to do more than 10 times the amount
of I/O it really has to do in the checksumming phase (which in the current
implementation, reads small ranges of partitions at a time).
This patch has two levels:
1. In the lower level, sstable::data_consume_rows(), which reads all
partitions in a given disk byte range, now gets another byte position,
"last_end". That can be the range's end, the end of the file, or anything
in between the two. It opens the disk stream until last_end, which means
1. we will never read-ahead beyond last_end, and 2. fast_fordward_to() is
not allowed beyond last_end.
2. In the upper level, we add to the various layers of sstable readers,
mutation readers, etc., a boolean flag mutation_reader::forwarding, which
says whether fast_forward_to() is allowed on the stream of mutations to
move the stream to a different partition range.
Note that this flag is separate from the existing boolean flag
streamed_mutation::fowarding - that one talks about skipping inside a
single partition, while the flag we are adding is about switching the
partition range being read. Most of the functions that previously
accepted streamed_mutation::forwarding now accept *also* the option
mutation_reader::forwarding. The exception are functions which are known
to read only a single partition, and not support fast_forward_to() a
different partition range.
We note that if mutation_reader::forwarding::no is requested, and
fast_forward_to() is forbidden, there is no point in reading anything
beyond the range's end, so data_consume_rows() is called with last_end as
the range's end. But if forwarding::yes is requested, we use the end of the
file as last_end, exactly like the code before this patch did.
Importantly, we note that the repair's partition reading code,
column_family::make_streaming_reader, uses mutation_reader::forwarding::no,
while the other existing reading code will use the default forwarding::yes.
In the future, we can further optimize the amount of bytes read from disk
by replacing forwarding::yes by an actual last partition that may ever be
read, and use its byte position as the last_end passed to data_consume_rows.
But we don't do this yet, and it's not a regression from the existing code,
which also opened the file input stream until the end of the file, and not
until the end of the range query. Moreover, such an improvement will not
improve of anything if the overall range is always very large, in which
case not over-reading at its end will not improve performance.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20170614072122.13473-1-nyh@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
So far, the only way to combine outputs of multiple readers was to use
combining reader. It is very general and, in particular, supports case
when the readers emit mutations from overlapping ranges.
However, we have cases (e.g. streaming) when we need to read from
several disjoint ranges. Combining reader is a suboptimal solution as it
requires to creating a reader for each range and ignores the fact that
they do not overlap.
This patch introduces multi_range_mutation_reader which takes a
mutation_source and a sorted set of disjoint ranges. Internally, it uses
mutation_reader::fast_forward_to() to move to the next range once the
current one is completed.
We want to be able to fast forward sstable readers. However, just
implementing fast_forward_to() for combined_reader is not enough as the
sstables we are reading from may need to change.
Following patches are going to introduce a combined sstable reader that
derives from combined_reader. To make that possible we first need to
make combined_reader public.
Signed-off-by: Paweł Dziepak <pdziepak@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 fixes the problem of multiple concurrent get_ranges calls.
Previously each call was invalidating the result of the previous
call. Now they don't step on each other foot.
Signed-off-by: Piotr Jastrzebski <piotr@scylladb.com>
While limiting the number of concurrently executing sstable readers reduces
our memory load, the queued readers, although consuming a small amount of
memory, can still grow without bounds.
To limit the damage, add two limits on the queue:
- a timeout, which is equal to the read timeout
- a queue length limit, which is equal to 2% of the shard memory divided
by an estimate of the queued request size (1kb)
Together, these limits bound the amount of memory needed by queued disk
requests in case the disk can't keep up.
Message-Id: <1467206055-30769-1-git-send-email-avi@scylladb.com>
A restricting_reader wraps a mutation_reader, and restricts it concurrency
using a provided semaphore; this allows controlling read concurrency, which
is important since reads can consume a lot of resources ((number of
participating sstables) * 128k after we have streaming mutations, and a lot
more before).
mutation_reader and streamed_mutation may use the same stream as a source
mutation_fragments and mutations themselves (this happens in sstable reader).
In such case asking for next streamed_mutation from mutation_reader would
invalidate all other streamed_mutations.
Signed-off-by: Paweł Dziepak <pdziepak@scylladb.com>
