When purging regular tombstone consult the min_live_timestamp, if available.
This is safe since we don't need to protect dead data from resurrection, as it is already dead.
For shadowable_tombstones, consult the min_memtable_live_row_marker_timestamp,
if available, otherwise fallback to the min_live_timestamp.
If we see in a view table a shadowable tombstone with time T, then in any row where the row marker's timestamp is higher than T the shadowable tombstone is completely ignored and it doesn't hide any data in any column, so the shadowable tombstone can be safely purged without any effect or risk resurrecting any deleted data.
In other words, rows which might cause problems for purging a shadowable tombstone with time T are rows with row markers older or equal T. So to know if a whole sstable can cause problems for shadowable tombstone of time T, we need to check if the sstable's oldest row marker (and not oldest column) is older or equal T. And the same check applies similarly to the memtable.
If both extended timestamp statistics are missing, fallback to the legacy (and inaccurate) min_timestamp.
Fixesscylladb/scylladb#20423Fixesscylladb/scylladb#20424
> [!NOTE]
> no backport needed at this time
> We may consider backport later on after given some soak time in master/enterprise
> since we do see tombstone accumulation in the field under some materialized views workloads
Closesscylladb/scylladb#20446
* github.com:scylladb/scylladb:
cql-pytest: add test_compaction_tombstone_gc
sstable_compaction_test: add mv_tombstone_purge_test
sstable_compaction_test: tombstone_purge_test: test that old deleted data do not inhibit tombstone garbage collection
sstable_compaction_test: tombstone_purge_test: add testlog debugging
sstable_compaction_test: tombstone_purge_test: make_expiring: use next_timestamp
sstable, compaction: add debug logging for extended min timestamp stats
compaction: get_max_purgeable_timestamp: use memtable and sstable extended timestamp stats
compaction: define max_purgeable_fn
tombstone: can_gc_fn: move declaration to compaction_garbage_collector.hh
sstables: scylla_metadata: add ext_timestamp_stats
compaction_group, storage_group, table_state: add extended timestamp stats getters
sstables, memtable: track live timestamps
memtable_encoding_stats_collector: update row_marker: do nothing if missing
before this change, we rely on `using namespace seastar` to use
`seastar::format()` without qualifying the `format()` with its
namespace. this works fine until we changed the parameter type
of format string `seastar::format()` from `const char*` to
`fmt::format_string<...>`. this change practically invited
`seastar::format()` to the club of `std::format()` and `fmt::format()`,
where all members accept a templated parameter as its `fmt`
parameter. and `seastar::format()` is not the best candidate anymore.
despite that argument-dependent lookup (ADT for short) favors the
function which is in the same namespace as its parameter, but
`using namespace` makes `seastar::format()` more competitive,
so both `std::format()` and `seastar::format()` are considered
as the condidates.
that is what is happening scylladb in quite a few caller sites of
`format()`, hence ADT is not able to tell which function the winner
in the name lookup:
```
/__w/scylladb/scylladb/mutation/mutation_fragment_stream_validator.cc:265:12: error: call to 'format' is ambiguous
265 | return format("{} ({}.{} {})", _name_view, s.ks_name(), s.cf_name(), s.id());
| ^~~~~~
/usr/bin/../lib/gcc/x86_64-redhat-linux/14/../../../../include/c++/14/format:4290:5: note: candidate function [with _Args = <const std::basic_string_view<char> &, const seastar::basic_sstring<char, unsigned int, 15> &, const seastar::basic_sstring<char, unsigned int, 15> &, const utils::tagged_uuid<table_id_tag> &>]
4290 | format(format_string<_Args...> __fmt, _Args&&... __args)
| ^
/__w/scylladb/scylladb/seastar/include/seastar/core/print.hh:143:1: note: candidate function [with A = <const std::basic_string_view<char> &, const seastar::basic_sstring<char, unsigned int, 15> &, const seastar::basic_sstring<char, unsigned int, 15> &, const utils::tagged_uuid<table_id_tag> &>]
143 | format(fmt::format_string<A...> fmt, A&&... a) {
| ^
```
in this change, we
change all `format()` to either `fmt::format()` or `seastar::format()`
with following rules:
- if the caller expects an `sstring` or `std::string_view`, change to
`seastar::format()`
- if the caller expects an `std::string`, change to `fmt::format()`.
because, `sstring::operator std::basic_string` would incur a deep
copy.
we will need another change to enable scylladb to compile with the
latest seastar. namely, to pass the format string as a templated
parameter down to helper functions which format their parameters.
to miminize the scope of this change, let's include that change when
bumping up the seastar submodule. as that change will depend on
the seastar change.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Before we add a new, is_shadowable, parameter to it.
And define global `can_always_purge` and `can_never_purge`
functions, a-la `always_gc` and `never_gc`.
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
When a reverse slice is provided, it is given in the native reverse
format. Thus the ranges will be returned in the same order as stored
in the slice.
Therefore there is no need to distinguish between get_ranges and
get_native_ranges. The latter one gets dropped and get_ranges returns
ranges in the same order as stored in the slice.
The reconcilable_result is built as it would be constructed for
forward read queries for tables with reversed order.
Mutations constructed for reversed queries are consumed forward.
Drop overloaded reversed functions that reverse read_command and
reconcilable_result directly and keep only those requiring smart
pointers. They are not used any more.
assert() is traditionally disabled in release builds, but not in
scylladb. This hasn't caused problems so far, but the latest abseil
release includes a commit [1] that causes a 1000 insn/op regression when
NDEBUG is not defined.
Clearly, we must move towards a build system where NDEBUG is defined in
release builds. But we can't just define it blindly without vetting
all the assert() calls, as some were written with the expectation that
they are enabled in release mode.
To solve the conundrum, change all assert() calls to a new SCYLLA_ASSERT()
macro in utils/assert.hh. This macro is always defined and is not conditional
on NDEBUG, so we can later (after vetting Seastar) enable NDEBUG in release
mode.
[1] 66ef711d68Closesscylladb/scylladb#20006
C++23 made std::unique_ptr constexpr. A side effect of this (presumably)
is that the compiler compiles it more eagerly, requiring the full definition
of the class in std::make_unique, while it previously was content with
finding the definition later.
One victim of this change is the default argument of make_reversing_reader;
define it earlier (by including its header) to build with C++23.
flat_mutation_reader_v2 was introduced in a pair of commits in 2021:
e3309322c3 "Clone flat_mutation_reader related classes into v2 variants"
08b5773c12 "Adapt flat_mutation_reader_v2 to the new version of the API"
as a replacement for flat_mutation_reader, using range_tombstone_change
instead of range_tombstone to represent represent range tombstones. See
those commits for more information.
The transition was incremental; the last use of the original
flat_mutation_reader was removed in 2022 in commit
026f8cc1e7 "db: Use mutation_partition_v2 in mvcc"
In turn, flat_mutation_reader was introduced in 2017 in commit
748205ca75 "Introduce flat_mutation_reader"
To transition from a mutation_reader that nested rows within
a partition in a separate stream, to a flat reader that streamed
partitions and rows in the same stream.
Here, we reclaim the original name and rename the awkward
flat_mutation_reader_v2 to mutation_reader.
Note that mutation_fragment_v2 remains since we still use the original
for compatibilty, sometimes.
Some notes about the transition:
- files were also renamed. In one case (flat_mutation_reader_test.cc), the
rename target already existed, so we rename to
mutation_reader_another_test.cc.
- a namespace 'mutation_reader' with two definitions existed (in
mutation_reader_fwd.hh). Its contents was folded into the mutation_reader
class. As a result, a few #includes had to be adjusted.
Closesscylladb/scylladb#19356
in theory, std::result_of_t should have been removed in C++20. and
std::invoke_result_t is available since C++17. thanks to libstdc++,
the tree is compiling. but we should not rely on this.
so, in this change, we replace all `std::result_of_t` with
`std::invoke_result_t`. actually, clang + libstdc++ is already warning
us like:
```
In file included from /home/runner/work/scylladb/scylladb/multishard_mutation_query.cc:9:
In file included from /home/runner/work/scylladb/scylladb/schema/schema_registry.hh:11:
In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/12/unordered_map:38:
Warning: /usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/12/type_traits:2624:5: warning: 'result_of<void (noop_compacted_fragments_consumer::*(noop_compacted_fragments_consumer &))()>' is deprecated: use 'std::invoke_result' instead [-Wdeprecated-declarations]
2624 | using result_of_t = typename result_of<_Tp>::type;
| ^
/home/runner/work/scylladb/scylladb/mutation/mutation_compactor.hh:518:43: note: in instantiation of template type alias 'result_of_t' requested here
518 | if constexpr (std::is_same_v<std::result_of_t<decltype(&GCConsumer::consume_end_of_stream)(GCConsumer&)>, void>) {
|
```
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#18835
when compiling with clang-tidy, it warngs:
```
[6/9] Building CXX object readers/CMakeFiles/readers.dir/multishard.cc.o
/home/kefu/dev/scylladb/readers/multishard.cc:84:53: warning: 'fut_and_result' used after it was moved [bugprone-use-after-move]
84 | auto result = std::get<1>(std::move(fut_and_result));
| ^
/home/kefu/dev/scylladb/readers/multishard.cc:79:34: note: move occurred here
79 | _read_ahead_future = std::get<0>(std::move(fut_and_result));
| ^
```
but this warning is but a false alarm, as we are not really moving away
the *whole* tuple, we are just move away an element from it. but
clang-tidy cannot tell which element we are actually moving. so, silence
both places of `std::move()`.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#18363
Our interval template started life as `range`, and was supported
wrapping to follow Cassandra's convention of wrapping around the
maximum token.
We later recognized that an interval type should usually be non-wrapping
and split it into wrapping_range and nonwrapping_range, with `range`
aliasing wrapping_range to preserve compatibility.
Even later, we realized the name was already taken by C++ ranges and
so renamed it to `interval`. Given that intervals are usually non-wrapping,
the default `interval` type is non-wrapping.
We can now simplify it further, recognizing that everyone assumes
that an interval is non-wrapping and so doesn't need the
nonwrapping_interval_designation. We just rename nonwrapping_interval
to `interval` and remove the type alias.
get0() dates back from the days where Seastar futures carried tuples, and
get0() was a way to get the first (and usually only) element. Now
it's a distraction, and Seastar is likely to deprecate and remove it.
Replace with seastar::future::get(), which does the same thing.
When the reader is currently paused, it is resumed, fast-forwarded, then
paused again. The fast forwarding part can throw and this will lead to
destroying the reader without it being closed first.
Add a try-catch surrounding this part in the code. Also mark
`maybe_pause()` and `do_pause()` as noexcept, to make it clear why
that part doesn't need to be in the try-catch.
Fixes: #16606Closesscylladb/scylladb#16630
reader_consumer_v2 being a noncopyable_function imposes a restriction
when stacking one interposer consumer on top of another.
Think for example of a token-based segregator on top of a timestamp
based one.
To achieve that, the interposer consumer creator must be reentrant,
such that the consumer can be created on each "channel", but today
the creator becomes unusable after first usage.
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
Fixes some typos as found by codespell run on the code.
In this commit, I was hoping to fix only comments, not user-visible alerts, output, etc.
Follow-up commits will take care of them.
Refs: https://github.com/scylladb/scylladb/issues/16255
Signed-off-by: Yaniv Kaul <yaniv.kaul@scylladb.com>
to have feature parity with `configure.py`. we won't need this
once we migrate to C++20 modules. but before that day comes, we
need to stick with C++ headers.
we generate a rule for each .hh files to create a corresponding
.cc and then compile it, in order to verify the self-containness of
that header. so the number of rule is quite large, to avoid the
unnecessary overhead. the check-header target is enabled only if
`Scylla_CHECK_HEADERS` option is enabled.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#15913
When next_partition() or fast_forward_to() is called. Instead of trying
to simulate a properly closed partition by injecting synthetic mutation
fragments to properly close it.
The fragment reader currently unconditionally forwards its buffer to the
passed-in partition range. Even if this range is
`query::full_partition_range`, this will involve dropping any fragments
up to the first partitions tart. This causes problems for test users who
intentionally create invalid fragment streams, that don't start with a
partition-start.
Refactor the reader to not do any modifications on the stream, when
neither slice, nor partition-range was passed by the user.
When wiring multi range reader with cleanup, I found that cleanup
wouldn't be able to release disk space of input SSTables earlier.
The reason is that multi range reader fast forward to the next range,
therefore it enables mutation_reader::forwarding, and as a result,
combined reader cannot release readers proactively as it cannot tell
for sure that the underlying reader is exhausted. It may have reached
EOS for the current range, but it may have data for the next one.
The concept of EOS actually only applies to the current range being
read. A reader that returned EOS will actually get out of this
state once the combined reader fast forward to the next range.
Therefore, only the underlying reader, i.e. the sstable reader,
can for certain know that the data source is completely exhausted,
given that tokens are read in monotonically increasing order.
For reversed reads, that's not true but fast forward to range
is not actually supported yet for it.
Today, the SSTable reader already knows that the underlying SSTable
was exhausted in fast_forward_to(), after it call index_reader's
advance_to(partition_range), therefore it disables subsequent
reads. We can take a step further and also check that the index
was exhausted, i.e. reached EOF.
So if the index is exhausted, and there's no partition to read
after the fast_forward_to() call, we know that there's nothing
left to do in this reader, and therefore the reader can be
closed proactively, allowing the disk space of SSTable to be
reclaimed if it was already deleted.
We can see that the combined reader, under multi range reader,
will incrementally find a set of disjoint SSTable exhausted,
as it fast foward to owned ranges
1:
INFO 2023-07-05 10:51:09,570 [shard 0] mutation_reader - flat_multi_range_mutation_reader(): fast forwarding to range [{-4525396453480898112, start},{-4525396453480898112, end}]
INFO 2023-07-05 10:51:09,570 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-1-big-Data.db, start == *end, eof ? true
INFO 2023-07-05 10:51:09,570 [shard 0] sstable - closing reader 0x60100029d800 for /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-1-big-Data.db
INFO 2023-07-05 10:51:09,570 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-3-big-Data.db, start == *end, eof ? false
INFO 2023-07-05 10:51:09,570 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-4-big-Data.db, start == *end, eof ? false
INFO 2023-07-05 10:51:09,570 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-5-big-Data.db, start == *end, eof ? false
INFO 2023-07-05 10:51:09,570 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-6-big-Data.db, start == *end, eof ? false
INFO 2023-07-05 10:51:09,570 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-7-big-Data.db, start == *end, eof ? false
INFO 2023-07-05 10:51:09,570 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-8-big-Data.db, start == *end, eof ? false
INFO 2023-07-05 10:51:09,570 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-9-big-Data.db, start == *end, eof ? false
INFO 2023-07-05 10:51:09,570 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-10-big-Data.db, start == *end, eof ? false
2:
INFO 2023-07-05 10:51:09,572 [shard 0] mutation_reader - flat_multi_range_mutation_reader(): fast forwarding to range [{-2253424581619911583, start},{-2253424581619911583, end}]
INFO 2023-07-05 10:51:09,572 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-2-big-Data.db, start == *end, eof ? true
INFO 2023-07-05 10:51:09,572 [shard 0] sstable - closing reader 0x60100029d400 for /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-2-big-Data.db
INFO 2023-07-05 10:51:09,572 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-4-big-Data.db, start == *end, eof ? false
INFO 2023-07-05 10:51:09,572 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-5-big-Data.db, start == *end, eof ? false
INFO 2023-07-05 10:51:09,572 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-6-big-Data.db, start == *end, eof ? false
INFO 2023-07-05 10:51:09,572 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-7-big-Data.db, start == *end, eof ? false
INFO 2023-07-05 10:51:09,572 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-8-big-Data.db, start == *end, eof ? false
INFO 2023-07-05 10:51:09,572 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-9-big-Data.db, start == *end, eof ? false
INFO 2023-07-05 10:51:09,572 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-10-big-Data.db, start == *end, eof ? false
And so on.
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
In mutation_reader_merger and clustering_order_reader_merger, the
operator()() is responsible for producing mutation fragments that will
be merged and pushed to the combined reader's buffer. Sometimes, it
might have to advance existing readers, open new and / or close some
existing ones, which requires calling a helper method and then calling
operator()() recursively.
In some unlucky circumstances, a stack overflow can occur:
- Readers have to be opened incrementally,
- Most or all readers must not produce any fragments and need to report
end of stream without preemption,
- There has to be enough readers opened within the lifetime of the
combined reader (~500),
- All of the above needs to happen within a single task quota.
In order to prevent such a situation, the code of both reader merger
classes were modified not to perform recursion at all. Most of the code
of the operator()() was moved to maybe_produce_batch which does not
recur if it is not possible for it to produce a fragment, instead it
returns std::nullopt and operator()() calls this method in a loop via
seastar::repeat_until_value.
A regression test is added.
Fixes: scylladb/scylladb#14415
Closes#14452
The evictable reader must ensure that each buffer fill makes forward
progress, i.e. the last fragment in the buffer has a position larger
than the last fragment from the previous buffer-fill. Otherwise, the
reader could get stuck in an infinite loop between buffer fills, if the
reader is evicted in-between.
The code guranteeing this forward progress had a bug: the comparison
between the position after the last buffer-fill and the current
last fragment position was done in the wrong direction.
So if the condition that we wanted to achieve was already true, we would
continue filling the buffer until partition end which may lead to OOMs
such as in #13491.
There was already a fix in this area to handle `partition_start`
fragments correctly - #13563 - but it missed that the position
comparison was done in the wrong order.
Fix the comparison and adjust one of the tests (added in #13563) to
detect this case.
Fixes#13491
This is not strictly necessary, as the multishard reader will be later
avoided altogether for tablet-based tables, but it is a step towards
converting all code to use the erm->get_sharder() instead of
schema::get_sharder().
In that level no io_priority_class-es exist. Instead, all the IO happens
in the context of current sched-group. File API no longer accepts prio
class argument (and makes io_intent arg mandatory to impls).
So the change consists of
- removing all usage of io_priority_class
- patching file_impl's inheritants to updated API
- priority manager goes away altogether
- IO bandwidth update is performed on respective sched group
- tune-up scylla-gdb.py io_queues command
The first change is huge and was made semi-autimatically by:
- grep io_priority_class | default_priority_class
- remove all calls, found methods' args and class' fields
Patching file_impl-s is smaller, but also mechanical:
- replace io_priority_class& argument with io_intent* one
- pass intent to lower file (if applicatble)
Dropping the priority manager is:
- git-rm .cc and .hh
- sed out all the #include-s
- fix configure.py and cmakefile
The scylla-gdb.py update is a bit hairry -- it needs to use task queues
list for IO classes names and shares, but to detect it should it checks
for the "commitlog" group is present.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
Closes#13963
The validator classes have their definition in a header located in mutation/,
while their implementation is located in a .cc in readers/mutation_reader.cc.
This patch fixes this inconsistency by moving the implementation into
mutation/mutation_fragment_stream_validator.cc. The only change is that
the validator code gets a new logger instance (but the logger variable itself
is left unchanged for now).
In addition to the data file itself. Currently validation avoids the
index altogether, using the crawling reader which only relies on the
data file and ignores the index+summary. This is because a corrupt
sstable usually has a corrupt index too and using both at the same time
might hide the corruption. This patch adds targeted validation of the
index, independent of and in addition to the already existing data
validation: it validates the order of index entries as well as whether
the entry points to a complete partition in the data file.
This will usually result in duplicate errors for out-of-order
partitions: one for the data file and one for the index file.
Fixes: #9611Closes#11405
* github.com:scylladb/scylladb:
test/cql-pytest: add test_sstable_validation.py
test/cql-pytest: extract scylla_path,temp_workdir fixtures to conftest.py
tools/scylla-sstables: write validation result to stdout
sstables/sstable: validate(): delegate to mx validator for mx sstables
sstables/mx/reader: add mx specific validator
mutation/mutation_fragment_stream_validator: add validator() accessor to validating filter
sstables/mx/reader: template data_consume_rows_context_m on the consumer
sstables/mx/reader: move row_processing_result to namespace scope
sstables/mx/reader: use data_consumer::proceed directly
sstables/mx/reader.cc: extend namespace to end-of-file (cosmetic)
compaction/compaction: remove now unused scrub_validate_mode_validate_reader()
compaction/compaction: move away from scrub_validate_mode_validate_reader()
tools/scylla-sstable: move away from scrub_validate_mode_validate_reader()
test/boost/sstable_compaction_test: move away from scrub_validate_mode_validate_reader()
sstables/sstable: add validate() method
compaction/compaction: scrub_sstables_validate_mode(): validate sstables one-by-one
compaction: scrub: use error messages from validator
mutation_fragment_stream_validator: produce error messages in low-level validator
In https://github.com/scylladb/scylladb/pull/13482 we renamed the reader permit states to more descriptive names. That PR however only covered only the states themselves and their usages, as well as the documentation in `docs/dev`.
This PR is a followup to said PR, completing the name changes: renaming all symbols, names, comments etc, so all is consistent and up-to-date.
Closes#13573
* github.com:scylladb/scylladb:
reader_concurrency_semaphore: misc updates w.r.t. recent permit state name changes
reader_concurrency_semaphore: update permit members w.r.t. recent permit state name changes
reader_concurrency_semaphore: update RAII state guard classes w.r.t. recent permit state name changes
reader_concurrency_semaphore: update API w.r.t. recent permit state name changes
reader_concurrency_semaphore: update stats w.r.t. recent permit state name changes
Currently, error messages for validation errors are produced in several
places:
* the high-level validator (which is built on the low-level one)
* scrub compaction and validation compaction (scrub in validate mode)
* scylla-sstable's validate operation
We plan to introduce yet another place which would use the low-level
validator and hence would have to produce its own error messages. To cut
down all this duplication, centralize the production of error messages
in the low-level validator, which now returns a `validation_result`
object instead of bool from its validate methods. This object can be
converted to bool (so its backwards compatible) and also contains an
error message if validation failed. In the next patches we will migrate
all users of the low level validator (be that direct or indirect) to use
the error messages provided in this result object instead of coming up
with one themselves.
The evictable reader must ensure that each buffer fill makes forward
progress, i.e. the last fragment in the buffer has a position larger
than the last fragment from the last buffer-fill. Otherwise, the reader
could get stuck in an infinite loop between buffer fills, if the reader
is evicted in-between.
The code guranteeing this forward change has a bug: when the next
expected position is a partition-start (another partition), the code
would loop forever, effectively reading all there is from the underlying
reader.
To avoid this, add a special case to ignore the progress guarantee loop
altogether when the next expected position is a partition start. In this
case, progress is garanteed anyway, because there is exactly one
partition-start fragment in each partition.
Fixes: #13491Closes#13563
When creating the reader, the lifecycle policy might return one that was
saved on the last page and survived in the cache. This reader might have
skipped some fast-forwarding ranges while sitting in the cache. To avoid
using a reader reading a stale range (from the read's POV), check its
read range and fast forward it if necessary.
And propagate it down to where it is created. This will be used to add
trace points for semaphore related events, but this will come in the
next patches.
A read that requested memory and has to wait for it can be registered as inactive. This can happen for example if the memory request originated from a background I/O operation (a read-ahead maybe).
Handling this case is currently very difficult. What we want to do is evict such a read on-the-spot: the fact that there is a read waiting on memory means memory is in demand and so inactive reads should be evicted. To evict this reader, we'd first have to remove it from the memory wait list, which is almost impossible currently, because `expiring_fifo<>`, the type used for the wait list, doesn't allow for that. So in this PR we set out to make this possible first, by transforming all current queues to be intrusive lists of permits. Permits are already linked into an intrusive list, to allow for enumerating all existing permits. We use these existing hooks to link the permits into the appropriate queue, and back to `_permit_list` when they are not in any special queue. To make this possible we first have to make all lists store naked permits, moving all auxiliary data fields currently stored in wrappers like `entry` into the permit itself. With this, all queues and lists in the semaphore are intrusive lists, storing permits directly, which has the following implications:
* queues no longer take extra memory, as all of them are intrusive
* permits are completely self-sufficient w.r.t to queuing: code can queue or dequeue permits just with a reference to a permit at hand, no other wrapper, iterator, pointer, etc. is necessary.
* queues don't keep permits alive anymore; destroying a permit will automatically unlink it from the respective queue, although this might lead to use-after-free. Not a problem in practice, only one code-path (`reader_concurrenc_semaphore::with_permit()`) had to be adjusted.
After all that extensive preparations, we can now handle the case of evicting a reader which is queued on memory.
Fixes: #12700Closes#12777
* github.com:scylladb/scylladb:
reader_concurrency_semaphore: handle reader blocked on memory becoming inactive
reader_concurrency_semaphore: move _permit_list next to the other lists
reader_permit: evict inactive read on timeout
reader_concurrency_semaphore: move inactive_read to .cc
reader_concurrency_semaphore: store permits in _inactive_reads
reader_concurrency_semaphore: inactive_read: de-inline more methods
reader_concurrency_semaphore: make _ready_list intrusive
reader_permit: add wait_for_execution state
reader_concurrency_semaphore: make wait lists intrusive
reader_concurrency_semaphore: move most wait_queue methods out-of-line
reader_concurrency_semaphore: store permits directly in queues
reader_permit: introduce (private) operator * and ->
reader_concurrency_semaphore: remove redundant waiters() member
reader_concurrency_semaphore: add waiters counter
reader_permit: use check_abort() for timeout
reader_concurrency_semaphore: maybe_dump_permit_diagnostics(): remove permit list param
reader_concurrency_semaphroe: make foreach_permit() const
reader_permit: add get_schema() and get_op_name() accessors
reader_concurrency_semaphore: mark maybe_dump_permit_diagnostics as noexcept
just came across this part of code, as `maybe_yield()` is a wrapper
around "if should_yield(): yield()", so better off using it for more
concise code.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closes#13107
Currently the reader_permit has some private methods that only the
semaphore's internal calls. But this method of communication is not
consistent, other times the semaphore accesses the permit impl directly,
calling methods on that.
This commit introduces operator * and -> for reader_permit. With this,
the semaphore internals always call the reader_permit::impl methods
direcly, either via a direct reference, or via the above operators.
This makes the permit internface a little narrower and reduces
boilerplate code.
Instead of having callers use get_timeout(), then compare it against the
current time, set up a timeout timer in the permit, which assigned a new
`_ex` member (a `std::exception_ptr`) to the appropriate exception type
when it fires.
Callers can now just poll check_abort() which will throw when `_ex`
is not null. This is more natural and allows for more general reasons
for aborting reads in the future.
This prepares the ground for timeouts being managed inside the permit,
instead of by the semaphore. Including timing out while in a wait queue.
The series fixes the `make_nonforwardable` reader, it shouldn't emit `partition_end` for previous partition after `next_partition()` and `fast_forward_to()`
Fixes: #12249Closes#12978
* github.com:scylladb/scylladb:
flat_mutation_reader_test: cleanup, seastar::async -> SEASTAR_THREAD_TEST_CASE
make_nonforwardable: test through run_mutation_source_tests
make_nonforwardable: next_partition and fast_forward_to when single_partition is true
make_forwardable: fix next_partition
flat_mutation_reader_v2: drop forward_buffer_to
nonforwardable reader: fix indentation
nonforwardable reader: refactor, extract reset_partition
nonforwardable reader: add more tests
nonforwardable reader: no partition_end after fast_forward_to()
nonforwardable reader: no partition_end after next_partition()
nonforwardable reader: no partition_end for empty reader
row_cache: pass partition_start though nonforwardable reader
This flag designates that we should consume only one
partition from the underlying reader. This means that
attempts to move to another partition should cause an EOS.
