a011a9ebf2
Add a dismantler functor parameter. When the multishard reader is destroyed this functor will be called for each shard reader, passing a future to a `stopped_foreign_reader`. This future becomes available when the shard reader is stopped, that is, when it finished all in-progress read-aheads and/or pending next partition calls. The intended use case for the dismantler functor is a client that needs to be notified when readers are destroyed and/or has to have access to any unconsumed fragments from the foreign readers wrapping the shard readers.
440 lines
21 KiB
C++
440 lines
21 KiB
C++
/*
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* Copyright (C) 2015 ScyllaDB
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*/
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/*
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* This file is part of Scylla.
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*
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* Scylla is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Affero General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* Scylla is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with Scylla. If not, see <http://www.gnu.org/licenses/>.
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*/
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#pragma once
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#include <vector>
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#include "mutation.hh"
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#include "clustering_key_filter.hh"
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#include "core/future.hh"
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#include "core/future-util.hh"
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#include "core/do_with.hh"
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#include "tracing/trace_state.hh"
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#include "flat_mutation_reader.hh"
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#include "reader_concurrency_semaphore.hh"
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namespace mutation_reader {
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// mutation_reader::forwarding determines whether fast_forward_to() may
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// be used on the mutation reader to change the partition range being
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// read. Enabling forwarding also changes read policy: forwarding::no
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// means we will stop reading from disk at the end of the given range,
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// but with forwarding::yes we may read ahead, anticipating the user to
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// make a small skip with fast_forward_to() and continuing to read.
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//
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// Note that mutation_reader::forwarding is similarly name but different
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// from streamed_mutation::forwarding - the former is about skipping to
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// a different partition range, while the latter is about skipping
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// inside a large partition.
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using forwarding = flat_mutation_reader::partition_range_forwarding;
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}
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class reader_selector {
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protected:
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schema_ptr _s;
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dht::ring_position_view _selector_position;
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public:
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reader_selector(schema_ptr s, dht::ring_position_view rpv) noexcept : _s(std::move(s)), _selector_position(std::move(rpv)) {}
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virtual ~reader_selector() = default;
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// Call only if has_new_readers() returned true.
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virtual std::vector<flat_mutation_reader> create_new_readers(const std::optional<dht::ring_position_view>& pos) = 0;
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virtual std::vector<flat_mutation_reader> fast_forward_to(const dht::partition_range& pr, db::timeout_clock::time_point timeout) = 0;
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// Can be false-positive but never false-negative!
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bool has_new_readers(const std::optional<dht::ring_position_view>& pos) const noexcept {
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dht::ring_position_comparator cmp(*_s);
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return !_selector_position.is_max() && (!pos || cmp(*pos, _selector_position) >= 0);
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}
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};
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// Creates a mutation reader which combines data return by supplied readers.
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// Returns mutation of the same schema only when all readers return mutations
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// of the same schema.
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flat_mutation_reader make_combined_reader(schema_ptr schema,
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std::vector<flat_mutation_reader>,
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streamed_mutation::forwarding fwd_sm = streamed_mutation::forwarding::no,
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mutation_reader::forwarding fwd_mr = mutation_reader::forwarding::yes);
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flat_mutation_reader make_combined_reader(schema_ptr schema,
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std::unique_ptr<reader_selector>,
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streamed_mutation::forwarding,
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mutation_reader::forwarding);
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flat_mutation_reader make_combined_reader(schema_ptr schema,
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flat_mutation_reader&& a,
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flat_mutation_reader&& b,
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streamed_mutation::forwarding fwd_sm = streamed_mutation::forwarding::no,
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mutation_reader::forwarding fwd_mr = mutation_reader::forwarding::yes);
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template <typename MutationFilter>
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GCC6_CONCEPT(
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requires requires(MutationFilter mf, const dht::decorated_key& dk) {
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{ mf(dk) } -> bool;
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}
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)
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class filtering_reader : public flat_mutation_reader::impl {
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flat_mutation_reader _rd;
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MutationFilter _filter;
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static_assert(std::is_same<bool, std::result_of_t<MutationFilter(const dht::decorated_key&)>>::value, "bad MutationFilter signature");
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public:
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filtering_reader(flat_mutation_reader rd, MutationFilter&& filter)
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: impl(rd.schema())
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, _rd(std::move(rd))
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, _filter(std::forward<MutationFilter>(filter)) {
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}
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virtual future<> fill_buffer(db::timeout_clock::time_point timeout) override {
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return do_until([this] { return is_buffer_full() || is_end_of_stream(); }, [this, timeout] {
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return _rd.fill_buffer(timeout).then([this] {
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while (!_rd.is_buffer_empty()) {
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auto mf = _rd.pop_mutation_fragment();
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if (mf.is_partition_start()) {
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auto& dk = mf.as_partition_start().key();
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if (!_filter(dk)) {
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_rd.next_partition();
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continue;
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}
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}
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push_mutation_fragment(std::move(mf));
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}
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_end_of_stream = _rd.is_end_of_stream();
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});
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});
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}
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virtual void next_partition() override {
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clear_buffer_to_next_partition();
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if (is_buffer_empty()) {
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_end_of_stream = false;
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_rd.next_partition();
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}
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}
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virtual future<> fast_forward_to(const dht::partition_range& pr, db::timeout_clock::time_point timeout) override {
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clear_buffer();
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_end_of_stream = false;
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return _rd.fast_forward_to(pr, timeout);
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}
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virtual future<> fast_forward_to(position_range pr, db::timeout_clock::time_point timeout) override {
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forward_buffer_to(pr.start());
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_end_of_stream = false;
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return _rd.fast_forward_to(std::move(pr), timeout);
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}
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virtual size_t buffer_size() const override {
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return flat_mutation_reader::impl::buffer_size() + _rd.buffer_size();
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}
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};
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// Creates a mutation_reader wrapper which creates a new stream of mutations
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// with some mutations removed from the original stream.
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// MutationFilter is a callable which decides which mutations are dropped. It
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// accepts mutation const& and returns a bool. The mutation stays in the
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// stream if and only if the filter returns true.
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template <typename MutationFilter>
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flat_mutation_reader make_filtering_reader(flat_mutation_reader rd, MutationFilter&& filter) {
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return make_flat_mutation_reader<filtering_reader<MutationFilter>>(std::move(rd), std::forward<MutationFilter>(filter));
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}
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/// A partition_presence_checker quickly returns whether a key is known not to exist
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/// in a data source (it may return false positives, but not false negatives).
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enum class partition_presence_checker_result {
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definitely_doesnt_exist,
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maybe_exists
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};
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using partition_presence_checker = std::function<partition_presence_checker_result (const dht::decorated_key& key)>;
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inline
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partition_presence_checker make_default_partition_presence_checker() {
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return [] (const dht::decorated_key&) { return partition_presence_checker_result::maybe_exists; };
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}
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// mutation_source represents source of data in mutation form. The data source
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// can be queried multiple times and in parallel. For each query it returns
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// independent mutation_reader.
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// The reader returns mutations having all the same schema, the one passed
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// when invoking the source.
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class mutation_source {
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using partition_range = const dht::partition_range&;
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using io_priority = const io_priority_class&;
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using flat_reader_factory_type = std::function<flat_mutation_reader(schema_ptr,
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partition_range,
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const query::partition_slice&,
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io_priority,
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tracing::trace_state_ptr,
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streamed_mutation::forwarding,
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mutation_reader::forwarding,
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reader_resource_tracker)>;
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// We could have our own version of std::function<> that is nothrow
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// move constructible and save some indirection and allocation.
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// Probably not worth the effort though.
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lw_shared_ptr<flat_reader_factory_type> _fn;
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lw_shared_ptr<std::function<partition_presence_checker()>> _presence_checker_factory;
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private:
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mutation_source() = default;
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explicit operator bool() const { return bool(_fn); }
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friend class optimized_optional<mutation_source>;
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public:
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mutation_source(flat_reader_factory_type fn, std::function<partition_presence_checker()> pcf = [] { return make_default_partition_presence_checker(); })
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: _fn(make_lw_shared(std::move(fn)))
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, _presence_checker_factory(make_lw_shared(std::move(pcf)))
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{ }
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mutation_source(std::function<flat_mutation_reader(schema_ptr, partition_range, const query::partition_slice&, io_priority,
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tracing::trace_state_ptr, streamed_mutation::forwarding, mutation_reader::forwarding)> fn,
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std::function<partition_presence_checker()> pcf = [] { return make_default_partition_presence_checker(); })
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: mutation_source([fn = std::move(fn)] (schema_ptr s,
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partition_range range,
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const query::partition_slice& slice,
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io_priority pc,
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tracing::trace_state_ptr tr,
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streamed_mutation::forwarding fwd,
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mutation_reader::forwarding fwd_mr,
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reader_resource_tracker) {
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return fn(s, range, slice, pc, std::move(tr), fwd, fwd_mr);
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}
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, std::move(pcf))
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{ }
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// For sources which don't care about the mutation_reader::forwarding flag (always fast forwardable)
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mutation_source(std::function<flat_mutation_reader(schema_ptr, partition_range, const query::partition_slice&, io_priority,
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tracing::trace_state_ptr, streamed_mutation::forwarding)> fn)
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: mutation_source([fn = std::move(fn)] (schema_ptr s,
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partition_range range,
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const query::partition_slice& slice,
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io_priority pc,
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tracing::trace_state_ptr tr,
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streamed_mutation::forwarding fwd,
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mutation_reader::forwarding,
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reader_resource_tracker) {
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return fn(s, range, slice, pc, std::move(tr), fwd);
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}) {}
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mutation_source(std::function<flat_mutation_reader(schema_ptr, partition_range, const query::partition_slice&, io_priority)> fn)
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: mutation_source([fn = std::move(fn)] (schema_ptr s,
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partition_range range,
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const query::partition_slice& slice,
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io_priority pc,
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tracing::trace_state_ptr,
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streamed_mutation::forwarding fwd,
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mutation_reader::forwarding,
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reader_resource_tracker) {
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assert(!fwd);
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return fn(s, range, slice, pc);
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}) {}
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mutation_source(std::function<flat_mutation_reader(schema_ptr, partition_range, const query::partition_slice&)> fn)
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: mutation_source([fn = std::move(fn)] (schema_ptr s,
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partition_range range,
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const query::partition_slice& slice,
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io_priority,
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tracing::trace_state_ptr,
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streamed_mutation::forwarding fwd,
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mutation_reader::forwarding,
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reader_resource_tracker) {
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assert(!fwd);
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return fn(s, range, slice);
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}) {}
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mutation_source(std::function<flat_mutation_reader(schema_ptr, partition_range range)> fn)
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: mutation_source([fn = std::move(fn)] (schema_ptr s,
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partition_range range,
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const query::partition_slice&,
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io_priority,
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tracing::trace_state_ptr,
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streamed_mutation::forwarding fwd,
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mutation_reader::forwarding,
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reader_resource_tracker) {
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assert(!fwd);
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return fn(s, range);
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}) {}
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mutation_source(const mutation_source& other) = default;
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mutation_source& operator=(const mutation_source& other) = default;
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mutation_source(mutation_source&&) = default;
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mutation_source& operator=(mutation_source&&) = default;
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// Creates a new reader.
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//
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// All parameters captured by reference must remain live as long as returned
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// mutation_reader or streamed_mutation obtained through it are alive.
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flat_mutation_reader
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make_reader(
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schema_ptr s,
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partition_range range,
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const query::partition_slice& slice,
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io_priority pc = default_priority_class(),
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tracing::trace_state_ptr trace_state = nullptr,
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streamed_mutation::forwarding fwd = streamed_mutation::forwarding::no,
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mutation_reader::forwarding fwd_mr = mutation_reader::forwarding::yes,
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reader_resource_tracker tracker = no_resource_tracking()) const
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{
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return (*_fn)(std::move(s), range, slice, pc, std::move(trace_state), fwd, fwd_mr, tracker);
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}
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flat_mutation_reader
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make_reader(
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schema_ptr s,
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partition_range range = query::full_partition_range) const
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{
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auto& full_slice = s->full_slice();
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return this->make_reader(std::move(s), range, full_slice);
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}
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partition_presence_checker make_partition_presence_checker() {
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return (*_presence_checker_factory)();
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}
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};
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// Returns a mutation_source which is the sum of given mutation_sources.
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//
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// Adding two mutation sources gives a mutation source which contains
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// the sum of writes contained in the addends.
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mutation_source make_combined_mutation_source(std::vector<mutation_source>);
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// Represent mutation_source which can be snapshotted.
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class snapshot_source {
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private:
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std::function<mutation_source()> _func;
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public:
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snapshot_source(std::function<mutation_source()> func)
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: _func(std::move(func))
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{ }
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// Creates a new snapshot.
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// The returned mutation_source represents all earlier writes and only those.
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// Note though that the mutations in the snapshot may get compacted over time.
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mutation_source operator()() {
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return _func();
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}
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};
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mutation_source make_empty_mutation_source();
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snapshot_source make_empty_snapshot_source();
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// Creates a restricted reader whose resource usages will be tracked
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// during it's lifetime. If there are not enough resources (dues to
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// existing readers) to create the new reader, it's construction will
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// be deferred until there are sufficient resources.
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// The internal reader once created will not be hindered in it's work
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// anymore. Reusorce limits are determined by the config which contains
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// a semaphore to track and limit the memory usage of readers. It also
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// contains a timeout and a maximum queue size for inactive readers
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// whose construction is blocked.
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flat_mutation_reader make_restricted_flat_reader(reader_concurrency_semaphore& semaphore,
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mutation_source ms,
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schema_ptr s,
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const dht::partition_range& range,
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const query::partition_slice& slice,
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const io_priority_class& pc = default_priority_class(),
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tracing::trace_state_ptr trace_state = nullptr,
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streamed_mutation::forwarding fwd = streamed_mutation::forwarding::no,
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mutation_reader::forwarding fwd_mr = mutation_reader::forwarding::yes);
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inline flat_mutation_reader make_restricted_flat_reader(reader_concurrency_semaphore& semaphore,
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mutation_source ms,
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schema_ptr s,
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const dht::partition_range& range = query::full_partition_range) {
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auto& full_slice = s->full_slice();
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return make_restricted_flat_reader(semaphore, std::move(ms), std::move(s), range, full_slice);
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}
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using mutation_source_opt = optimized_optional<mutation_source>;
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// Adapts a non-movable FlattenedConsumer to a movable one.
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template<typename FlattenedConsumer>
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class stable_flattened_mutations_consumer {
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std::unique_ptr<FlattenedConsumer> _ptr;
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public:
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stable_flattened_mutations_consumer(std::unique_ptr<FlattenedConsumer> ptr) : _ptr(std::move(ptr)) {}
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auto consume_new_partition(const dht::decorated_key& dk) { return _ptr->consume_new_partition(dk); }
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auto consume(tombstone t) { return _ptr->consume(t); }
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auto consume(static_row&& sr) { return _ptr->consume(std::move(sr)); }
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auto consume(clustering_row&& cr) { return _ptr->consume(std::move(cr)); }
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auto consume(range_tombstone&& rt) { return _ptr->consume(std::move(rt)); }
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auto consume_end_of_partition() { return _ptr->consume_end_of_partition(); }
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auto consume_end_of_stream() { return _ptr->consume_end_of_stream(); }
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};
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template<typename FlattenedConsumer, typename... Args>
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stable_flattened_mutations_consumer<FlattenedConsumer> make_stable_flattened_mutations_consumer(Args&&... args) {
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return { std::make_unique<FlattenedConsumer>(std::forward<Args>(args)...) };
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}
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/// Make a foreign_reader.
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///
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/// foreign_reader is a local representant of a reader located on a remote
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/// shard. Manages its lifecycle and takes care of seamlessly transferring
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/// produced fragments. Fragments are *copied* between the shards, a
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/// bufferful at a time.
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/// To maximize throughput read-ahead is used. After each fill_buffer() or
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/// fast_forward_to() a read-ahead (a fill_buffer() on the remote reader) is
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/// issued. This read-ahead runs in the background and is brough back to
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/// foreground on the next fill_buffer() or fast_forward_to() call.
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/// If the reader resides on this shard (the shard where make_foreign_reader()
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/// is called) there is no need to wrap it in foreign_reader, just return it as
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/// is.
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flat_mutation_reader make_foreign_reader(schema_ptr schema,
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foreign_ptr<std::unique_ptr<flat_mutation_reader>> reader,
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streamed_mutation::forwarding fwd_sm = streamed_mutation::forwarding::no);
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using remote_reader_factory = noncopyable_function<future<foreign_ptr<std::unique_ptr<flat_mutation_reader>>>(unsigned,
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schema_ptr,
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const dht::partition_range&,
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const query::partition_slice&,
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const io_priority_class&,
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tracing::trace_state_ptr,
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streamed_mutation::forwarding,
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mutation_reader::forwarding)>;
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struct stopped_foreign_reader {
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foreign_ptr<std::unique_ptr<flat_mutation_reader>> remote_reader;
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circular_buffer<mutation_fragment> unconsumed_fragments;
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};
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using foreign_reader_dismantler = noncopyable_function<void(shard_id, future<stopped_foreign_reader>)>;
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/// Make a multishard_combining_reader.
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///
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/// multishard_combining_reader takes care of reading a range from all shards
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/// that own a subrange in the range. Readers are created on-demand with the
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/// supplied reader_factory. This factory function is expected to create an
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/// appropriate reader on the specified shard and return a foreign_ptr to it.
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///
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/// The read starts with a concurrency of one, that is the reader reads from a
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/// single shard at a time. The concurrency is exponentially increased (to a
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/// maximum of the number of shards) when a reader's buffer is empty after
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/// moving the next shard. This condition is important as we only wan't to
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/// increase concurrency for sparse tables that have little data and the reader
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/// has to move between shards often. When concurrency is > 1, the reader
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/// issues background read-aheads to the next shards so that by the time it
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/// needs to move to them they have the data ready.
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/// For dense tables (where we rarely cross shards) we rely on the
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/// foreign_reader to issue sufficient read-aheads on its own to avoid blocking.
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///
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/// Optionally a dismantler function can be passed to the multishard
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/// reader. When the multishard reader is destroyed it will invoke the
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/// dismantler functor for each of its foreign (shard) readers, passing a future
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/// to a `stopped_foreign_reader`. The future becomes available when the foreign
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/// reader has stopped, that is, it finished all of its in-progress read aheads
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/// and/or any pending `next_partition()` calls.
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flat_mutation_reader make_multishard_combining_reader(schema_ptr schema,
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const dht::partition_range& pr,
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const query::partition_slice& ps,
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const io_priority_class& pc,
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const dht::i_partitioner& partitioner,
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remote_reader_factory reader_factory,
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tracing::trace_state_ptr trace_state = nullptr,
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streamed_mutation::forwarding fwd_sm = streamed_mutation::forwarding::no,
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mutation_reader::forwarding fwd_mr = mutation_reader::forwarding::no,
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foreign_reader_dismantler reader_dismantler = {});
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