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scylladb/row_cache.cc
Tomasz Grabiec d22fdf4261 row_cache: Improve safety of cache updates 
Cache imposes requirements on how updates to the on-disk mutation source
are made:
  1) each change to the on-disk muation source must be followed
     by cache synchronization reflecting that change
  2) The two must be serialized with other synchronizations
  3) must have strong failure guarantees (atomicity)

Because of that, sstable list update and cache synchronization must be
done under a lock, and cache synchronization cannot fail to synchronize.

Normally cache synchronization achieves no-failure thing by wiping the
cache (which is noexcept) in case failure is detect. There are some
setup steps hoever which cannot be skipped, e.g. taking a lock
followed by switching cache to use the new snapshot. That truly cannot
fail.  The lock inside cache synchronizers is redundant, since the
user needs to take it anyway around the combined operation.

In order to make ensuring strong exception guarantees easier, and
making the cache interface easier to use correctly, this patch moves
the control of the combined update into the cache. This is done by
having cache::update() et al accept a callback (external_updater)
which is supposed to perform modiciation of the underlying mutation
source when invoked.

This is in-line with the layering. Cache is layered on top of the
on-disk mutation source (it wraps it) and reading has to go through
cache. After the patch, modification also goes through cache. This way
more of cache's requirements can be confined to its implementation.

The failure semantics of update() and other synchronizers needed to
change due to strong exception guaratnees. Now if it fails, it means
the update was not performed, neither to the cache nor to the
underlying mutation source.

The database::_cache_update_sem goes away, serialization is done
internally by the cache.

The external_updater needs to have strong exception guarantees. This
requirement is not new. It is however currently violated in some
places. This patch marks those callbacks as noexcept and leaves a
FIXME. Those should be fixed, but that's not in the scope of this
patch. Aborting is still better than corrupting the state.

Fixes #2754.

Also fixes the following test failure:

  tests/row_cache_test.cc(949): fatal error: in "test_update_failure": critical check it->second.equal(*s, mopt->partition()) has failed

which started to trigger after commit 318423d50b. Thread stack
allocation may fail, in which case we did not do the necessary
invalidation.
2017-09-04 10:04:29 +02:00

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/*
* Copyright (C) 2015 ScyllaDB
*/
/*
* This file is part of Scylla.
*
* Scylla is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* Scylla is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with Scylla. If not, see <http://www.gnu.org/licenses/>.
*/
#include "row_cache.hh"
#include "core/memory.hh"
#include "core/do_with.hh"
#include "core/future-util.hh"
#include <seastar/core/metrics.hh>
#include <seastar/util/defer.hh>
#include "memtable.hh"
#include "partition_snapshot_reader.hh"
#include <chrono>
#include "utils/move.hh"
#include <boost/version.hpp>
#include <sys/sdt.h>
#include "stdx.hh"
#include "cache_streamed_mutation.hh"
#include "read_context.hh"
#include "schema_upgrader.hh"
using namespace std::chrono_literals;
using namespace cache;
static logging::logger clogger("cache");
thread_local seastar::thread_scheduling_group row_cache::_update_thread_scheduling_group(1ms, 0.2);
mutation_reader
row_cache::create_underlying_reader(read_context& ctx, mutation_source& src, const dht::partition_range& pr) {
ctx.on_underlying_created();
return src(_schema, pr, ctx.slice(), ctx.pc(), ctx.trace_state(), streamed_mutation::forwarding::yes);
}
cache_tracker& global_cache_tracker() {
static thread_local cache_tracker instance;
return instance;
}
cache_tracker::cache_tracker() {
setup_metrics();
_region.make_evictable([this] {
return with_allocator(_region.allocator(), [this] {
// Removing a partition may require reading large keys when we rebalance
// the rbtree, so linearize anything we read
return with_linearized_managed_bytes([&] {
try {
auto evict_last = [this](lru_type& lru) {
cache_entry& ce = lru.back();
auto it = row_cache::partitions_type::s_iterator_to(ce);
clear_continuity(*std::next(it));
lru.pop_back_and_dispose(current_deleter<cache_entry>());
};
if (_lru.empty()) {
return memory::reclaiming_result::reclaimed_nothing;
}
evict_last(_lru);
--_stats.partitions;
++_stats.partition_evictions;
++_stats.modification_count;
return memory::reclaiming_result::reclaimed_something;
} catch (std::bad_alloc&) {
// Bad luck, linearization during partition removal caused us to
// fail. Drop the entire cache so we can make forward progress.
clear();
return memory::reclaiming_result::reclaimed_something;
}
});
});
});
}
cache_tracker::~cache_tracker() {
clear();
}
void
cache_tracker::setup_metrics() {
namespace sm = seastar::metrics;
_metrics.add_group("cache", {
sm::make_gauge("bytes_used", sm::description("current bytes used by the cache out of the total size of memory"), [this] { return _region.occupancy().used_space(); }),
sm::make_gauge("bytes_total", sm::description("total size of memory for the cache"), [this] { return _region.occupancy().total_space(); }),
sm::make_derive("partition_hits", sm::description("number of partitions needed by reads and found in cache"), _stats.partition_hits),
sm::make_derive("partition_misses", sm::description("number of partitions needed by reads and missing in cache"), _stats.partition_misses),
sm::make_derive("partition_insertions", sm::description("total number of partitions added to cache"), _stats.partition_insertions),
sm::make_derive("row_hits", sm::description("total number of rows needed by reads and found in cache"), _stats.row_hits),
sm::make_derive("row_misses", sm::description("total number of rows needed by reads and missing in cache"), _stats.row_misses),
sm::make_derive("row_insertions", sm::description("total number of rows added to cache"), _stats.row_insertions),
sm::make_derive("concurrent_misses_same_key", sm::description("total number of operation with misses same key"), _stats.concurrent_misses_same_key),
sm::make_derive("partition_merges", sm::description("total number of partitions merged"), _stats.partition_merges),
sm::make_derive("partition_evictions", sm::description("total number of evicted partitions"), _stats.partition_evictions),
sm::make_derive("partition_removals", sm::description("total number of invalidated partitions"), _stats.partition_removals),
sm::make_derive("mispopulations", sm::description("number of entries not inserted by reads"), _stats.mispopulations),
sm::make_gauge("partitions", sm::description("total number of cached partitions"), _stats.partitions),
sm::make_derive("reads", sm::description("number of started reads"), _stats.reads),
sm::make_derive("reads_with_misses", sm::description("number of reads which had to read from sstables"), _stats.reads_with_misses),
sm::make_gauge("active_reads", sm::description("number of currently active reads"), [this] { return _stats.active_reads(); }),
sm::make_derive("sstable_reader_recreations", sm::description("number of times sstable reader was recreated due to memtable flush"), _stats.underlying_recreations),
sm::make_derive("sstable_partition_skips", sm::description("number of times sstable reader was fast forwarded across partitions"), _stats.underlying_partition_skips),
sm::make_derive("sstable_row_skips", sm::description("number of times sstable reader was fast forwarded within a partition"), _stats.underlying_row_skips),
});
}
void cache_tracker::clear() {
with_allocator(_region.allocator(), [this] {
auto clear = [this] (lru_type& lru) {
while (!lru.empty()) {
cache_entry& ce = lru.back();
auto it = row_cache::partitions_type::s_iterator_to(ce);
while (it->is_evictable()) {
cache_entry& to_remove = *it;
++it;
to_remove._lru_link.unlink();
current_deleter<cache_entry>()(&to_remove);
}
clear_continuity(*it);
}
};
clear(_lru);
});
_stats.partition_removals += _stats.partitions;
_stats.partitions = 0;
++_stats.modification_count;
}
void cache_tracker::touch(cache_entry& e) {
auto move_to_front = [this] (lru_type& lru, cache_entry& e) {
lru.erase(lru.iterator_to(e));
lru.push_front(e);
};
move_to_front(_lru, e);
}
void cache_tracker::insert(cache_entry& entry) {
++_stats.partition_insertions;
++_stats.partitions;
++_stats.modification_count;
_lru.push_front(entry);
}
void cache_tracker::on_erase() {
--_stats.partitions;
++_stats.partition_removals;
++_stats.modification_count;
}
void cache_tracker::on_merge() {
++_stats.partition_merges;
}
void cache_tracker::on_partition_hit() {
++_stats.partition_hits;
}
void cache_tracker::on_partition_miss() {
++_stats.partition_misses;
}
void cache_tracker::on_row_hit() {
++_stats.row_hits;
}
void cache_tracker::on_row_miss() {
++_stats.row_misses;
}
void cache_tracker::on_mispopulate() {
++_stats.mispopulations;
}
void cache_tracker::on_miss_already_populated() {
++_stats.concurrent_misses_same_key;
}
allocation_strategy& cache_tracker::allocator() {
return _region.allocator();
}
logalloc::region& cache_tracker::region() {
return _region;
}
const logalloc::region& cache_tracker::region() const {
return _region;
}
// Stable cursor over partition entries from given range.
//
// Must be accessed with reclaim lock held on the cache region.
// The position of the cursor is always valid, but cache entry reference
// is not always valid. It remains valid as long as the iterators
// into _cache._partitions remain valid. Cache entry reference can be
// brought back to validity by calling refresh().
//
class partition_range_cursor final {
std::reference_wrapper<row_cache> _cache;
row_cache::partitions_type::iterator _it;
row_cache::partitions_type::iterator _end;
dht::ring_position_view _start_pos;
dht::ring_position_view _end_pos;
stdx::optional<dht::decorated_key> _last;
uint64_t _last_reclaim_count;
size_t _last_modification_count;
private:
void set_position(cache_entry& e) {
// FIXME: make ring_position_view convertible to ring_position, so we can use e.position()
if (e.is_dummy_entry()) {
_last = {};
_start_pos = dht::ring_position_view::max();
} else {
_last = e.key();
_start_pos = dht::ring_position_view(*_last);
}
}
public:
// Creates a cursor positioned at the lower bound of the range.
// The cache entry reference is not valid.
// The range reference must remain live as long as this instance is used.
partition_range_cursor(row_cache& cache, const dht::partition_range& range)
: _cache(cache)
, _start_pos(dht::ring_position_view::for_range_start(range))
, _end_pos(dht::ring_position_view::for_range_end(range))
, _last_reclaim_count(std::numeric_limits<uint64_t>::max())
, _last_modification_count(std::numeric_limits<size_t>::max())
{ }
// Ensures that cache entry reference is valid.
// The cursor will point at the first entry with position >= the current position.
// Returns true if and only if the position of the cursor changed.
// Strong exception guarantees.
bool refresh() {
auto reclaim_count = _cache.get().get_cache_tracker().region().reclaim_counter();
auto modification_count = _cache.get().get_cache_tracker().modification_count();
if (reclaim_count == _last_reclaim_count && modification_count == _last_modification_count) {
return true;
}
auto cmp = cache_entry::compare(_cache.get()._schema);
if (cmp(_end_pos, _start_pos)) { // next() may have moved _start_pos past the _end_pos.
_end_pos = _start_pos;
}
_end = _cache.get()._partitions.lower_bound(_end_pos, cmp);
_it = _cache.get()._partitions.lower_bound(_start_pos, cmp);
auto same = !cmp(_start_pos, _it->position());
set_position(*_it);
_last_reclaim_count = reclaim_count;
_last_modification_count = modification_count;
return same;
}
// Positions the cursor at the next entry.
// May advance past the requested range. Use in_range() after the call to determine that.
// Call only when in_range() and cache entry reference is valid.
// Strong exception guarantees.
void next() {
auto next = std::next(_it);
set_position(*next);
_it = std::move(next);
}
// Valid only after refresh() and before _cache._partitions iterators are invalidated.
// Points inside the requested range if in_range().
cache_entry& entry() {
return *_it;
}
// Call only when cache entry reference is valid.
bool in_range() {
return _it != _end;
}
// Returns current position of the cursor.
// Result valid as long as this instance is valid and not advanced.
dht::ring_position_view position() const {
return _start_pos;
}
};
future<> read_context::create_sm() {
if (_range_query) {
// FIXME: Singular-range mutation readers don't support fast_forward_to(), so need to use a wide range
// here in case the same reader will need to be fast forwarded later.
_sm_range = dht::partition_range({dht::ring_position(*_key)}, {dht::ring_position(*_key)});
} else {
_sm_range = dht::partition_range::make_singular({dht::ring_position(*_key)});
}
return _underlying.fast_forward_to(std::move(_sm_range), *_underlying_snapshot, _phase).then([this] {
return _underlying.read_next_same_phase().then([this] (auto&& smo) {
if (!smo) {
_sm = make_empty_streamed_mutation(_cache.schema(), *_key, streamed_mutation::forwarding::yes);
} else {
_sm = std::move(*smo);
}
});
});
}
static streamed_mutation read_directly_from_underlying(streamed_mutation&& sm, read_context& reader) {
if (reader.schema()->version() != sm.schema()->version()) {
sm = transform(std::move(sm), schema_upgrader(reader.schema()));
}
if (reader.fwd() == streamed_mutation::forwarding::no) {
sm = streamed_mutation_from_forwarding_streamed_mutation(std::move(sm));
}
return std::move(sm);
}
// Reader which populates the cache using data from the delegate.
class single_partition_populating_reader final : public mutation_reader::impl {
row_cache& _cache;
mutation_reader _delegate;
lw_shared_ptr<read_context> _read_context;
public:
single_partition_populating_reader(row_cache& cache,
lw_shared_ptr<read_context> context)
: _cache(cache)
, _read_context(std::move(context))
{ }
virtual future<streamed_mutation_opt> operator()() override {
if (!_read_context) {
return make_ready_future<streamed_mutation_opt>(streamed_mutation_opt());
}
auto src_and_phase = _cache.snapshot_of(_read_context->range().start()->value());
auto phase = src_and_phase.phase;
_delegate = _cache.create_underlying_reader(*_read_context, src_and_phase.snapshot, _read_context->range());
return _delegate().then([this, phase] (auto sm) mutable -> streamed_mutation_opt {
auto ctx = std::move(_read_context);
if (!sm) {
return std::move(sm);
}
if (phase == _cache.phase_of(ctx->range().start()->value())) {
return _cache._read_section(_cache._tracker.region(), [&] {
cache_entry& e = _cache.find_or_create(sm->decorated_key(), sm->partition_tombstone(), phase);
return e.read(_cache, *ctx, std::move(*sm), phase);
});
} else {
_cache._tracker.on_mispopulate();
return read_directly_from_underlying(std::move(*sm), *ctx);
}
});
}
};
void cache_tracker::clear_continuity(cache_entry& ce) {
ce.set_continuous(false);
}
void row_cache::on_partition_hit() {
_tracker.on_partition_hit();
}
void row_cache::on_partition_miss() {
_tracker.on_partition_miss();
}
void row_cache::on_row_hit() {
_stats.hits.mark();
_tracker.on_row_hit();
}
void row_cache::on_mispopulate() {
_tracker.on_mispopulate();
}
void row_cache::on_row_miss() {
_stats.misses.mark();
_tracker.on_row_miss();
}
void row_cache::on_row_insert() {
++_tracker._stats.row_insertions;
}
class range_populating_reader {
row_cache& _cache;
autoupdating_underlying_reader& _reader;
stdx::optional<row_cache::previous_entry_pointer> _last_key;
read_context& _read_context;
private:
bool can_set_continuity() const {
return _last_key && _reader.creation_phase() == _cache.phase_of(_reader.population_range_start());
}
void handle_end_of_stream() {
if (!can_set_continuity()) {
_cache.on_mispopulate();
return;
}
if (!_reader.range().end() || !_reader.range().end()->is_inclusive()) {
cache_entry::compare cmp(_cache._schema);
auto it = _reader.range().end() ? _cache._partitions.find(_reader.range().end()->value(), cmp)
: std::prev(_cache._partitions.end());
if (it != _cache._partitions.end()) {
if (it == _cache._partitions.begin()) {
if (!_last_key->_key) {
it->set_continuous(true);
} else {
_cache.on_mispopulate();
}
} else {
auto prev = std::prev(it);
if (prev->key().equal(*_cache._schema, *_last_key->_key)) {
it->set_continuous(true);
} else {
_cache.on_mispopulate();
}
}
}
}
}
public:
range_populating_reader(row_cache& cache, read_context& ctx)
: _cache(cache)
, _reader(ctx.underlying())
, _read_context(ctx)
{}
future<streamed_mutation_opt> operator()() {
return _reader().then([this] (streamed_mutation_opt smopt) mutable -> streamed_mutation_opt {
{
if (!smopt) {
handle_end_of_stream();
return std::move(smopt);
}
_cache.on_partition_miss();
if (_reader.creation_phase() == _cache.phase_of(smopt->decorated_key())) {
return _cache._read_section(_cache._tracker.region(), [&] {
cache_entry& e = _cache.find_or_create(smopt->decorated_key(), smopt->partition_tombstone(), _reader.creation_phase(),
can_set_continuity() ? &*_last_key : nullptr);
_last_key = row_cache::previous_entry_pointer(smopt->decorated_key());
return e.read(_cache, _read_context, std::move(*smopt), _reader.creation_phase());
});
} else {
_cache._tracker.on_mispopulate();
_last_key = row_cache::previous_entry_pointer(smopt->decorated_key());
return read_directly_from_underlying(std::move(*smopt), _read_context);
}
}
});
}
future<> fast_forward_to(dht::partition_range&& pr) {
if (!pr.start()) {
_last_key = row_cache::previous_entry_pointer();
} else if (!pr.start()->is_inclusive() && pr.start()->value().has_key()) {
_last_key = row_cache::previous_entry_pointer(pr.start()->value().as_decorated_key());
} else {
// Inclusive start bound, cannot set continuity flag.
_last_key = {};
}
return _reader.fast_forward_to(std::move(pr));
}
};
class scanning_and_populating_reader final : public mutation_reader::impl {
const dht::partition_range* _pr;
row_cache& _cache;
lw_shared_ptr<read_context> _read_context;
partition_range_cursor _primary;
range_populating_reader _secondary_reader;
bool _secondary_in_progress = false;
bool _advance_primary = false;
stdx::optional<dht::partition_range::bound> _lower_bound;
dht::partition_range _secondary_range;
private:
streamed_mutation read_from_entry(cache_entry& ce) {
_cache.upgrade_entry(ce);
_cache._tracker.touch(ce);
_cache.on_partition_hit();
return ce.read(_cache, *_read_context);
}
streamed_mutation_opt do_read_from_primary() {
return _cache._read_section(_cache._tracker.region(), [this] {
return with_linearized_managed_bytes([&] () -> streamed_mutation_opt {
auto not_moved = _primary.refresh();
if (_advance_primary && not_moved) {
_primary.next();
not_moved = false;
}
_advance_primary = false;
if (not_moved || _primary.entry().continuous()) {
if (!_primary.in_range()) {
return stdx::nullopt;
}
cache_entry& e = _primary.entry();
auto sm = read_from_entry(e);
_lower_bound = dht::partition_range::bound{e.key(), false};
// Delay the call to next() so that we don't see stale continuity on next invocation.
_advance_primary = true;
return streamed_mutation_opt(std::move(sm));
} else {
if (_primary.in_range()) {
cache_entry& e = _primary.entry();
_secondary_range = dht::partition_range(_lower_bound ? std::move(_lower_bound) : _pr->start(),
dht::partition_range::bound{e.key(), false});
_lower_bound = dht::partition_range::bound{e.key(), true};
_secondary_in_progress = true;
return stdx::nullopt;
} else {
dht::ring_position_comparator cmp(*_read_context->schema());
auto range = _pr->trim_front(std::move(_lower_bound), cmp);
if (!range) {
return stdx::nullopt;
}
_lower_bound = dht::partition_range::bound{dht::ring_position::max()};
_secondary_range = std::move(*range);
_secondary_in_progress = true;
return stdx::nullopt;
}
}
});
});
}
future<streamed_mutation_opt> read_from_primary() {
auto smo = do_read_from_primary();
if (!_secondary_in_progress) {
return make_ready_future<streamed_mutation_opt>(std::move(smo));
}
return _secondary_reader.fast_forward_to(std::move(_secondary_range)).then([this] {
return read_from_secondary();
});
}
future<streamed_mutation_opt> read_from_secondary() {
return _secondary_reader().then([this] (streamed_mutation_opt smopt) {
if (smopt) {
return make_ready_future<streamed_mutation_opt>(std::move(smopt));
} else {
_secondary_in_progress = false;
return read_from_primary();
}
});
}
public:
scanning_and_populating_reader(row_cache& cache,
const dht::partition_range& range,
lw_shared_ptr<read_context> context)
: _pr(&range)
, _cache(cache)
, _read_context(std::move(context))
, _primary(cache, range)
, _secondary_reader(cache, *_read_context)
{ }
future<streamed_mutation_opt> operator()() {
if (_secondary_in_progress) {
return read_from_secondary();
} else {
return read_from_primary();
}
}
future<> fast_forward_to(const dht::partition_range& pr) {
_secondary_in_progress = false;
_advance_primary = false;
_pr = &pr;
_primary = partition_range_cursor{_cache, pr};
_lower_bound = {};
return make_ready_future<>();
}
};
mutation_reader
row_cache::make_scanning_reader(const dht::partition_range& range, lw_shared_ptr<read_context> context) {
return make_mutation_reader<scanning_and_populating_reader>(*this, range, std::move(context));
}
mutation_reader
row_cache::make_reader(schema_ptr s,
const dht::partition_range& range,
const query::partition_slice& slice,
const io_priority_class& pc,
tracing::trace_state_ptr trace_state,
streamed_mutation::forwarding fwd,
mutation_reader::forwarding fwd_mr)
{
auto ctx = make_lw_shared<read_context>(*this, std::move(s), range, slice, pc, trace_state, fwd, fwd_mr);
if (!ctx->is_range_query()) {
return _read_section(_tracker.region(), [&] {
return with_linearized_managed_bytes([&] {
cache_entry::compare cmp(_schema);
auto&& pos = ctx->range().start()->value();
auto i = _partitions.lower_bound(pos, cmp);
if (i != _partitions.end() && !cmp(pos, i->position())) {
cache_entry& e = *i;
_tracker.touch(e);
upgrade_entry(e);
on_partition_hit();
return make_reader_returning(e.read(*this, *ctx));
} else if (i->continuous()) {
return make_empty_reader();
} else {
on_partition_miss();
return make_mutation_reader<single_partition_populating_reader>(*this, std::move(ctx));
}
});
});
}
return make_scanning_reader(range, std::move(ctx));
}
row_cache::~row_cache() {
with_allocator(_tracker.allocator(), [this] {
_partitions.clear_and_dispose([this, deleter = current_deleter<cache_entry>()] (auto&& p) mutable {
if (!p->is_dummy_entry()) {
_tracker.on_erase();
}
deleter(p);
});
});
}
void row_cache::clear_now() noexcept {
with_allocator(_tracker.allocator(), [this] {
auto it = _partitions.erase_and_dispose(_partitions.begin(), partitions_end(), [this, deleter = current_deleter<cache_entry>()] (auto&& p) mutable {
_tracker.on_erase();
deleter(p);
});
_tracker.clear_continuity(*it);
});
}
template<typename CreateEntry, typename VisitEntry>
//requires requires(CreateEntry create, VisitEntry visit, row_cache::partitions_type::iterator it) {
// { create(it) } -> row_cache::partitions_type::iterator;
// { visit(it) } -> void;
// }
cache_entry& row_cache::do_find_or_create_entry(const dht::decorated_key& key,
const previous_entry_pointer* previous, CreateEntry&& create_entry, VisitEntry&& visit_entry)
{
return with_allocator(_tracker.allocator(), [&] () -> cache_entry& {
return with_linearized_managed_bytes([&] () -> cache_entry& {
auto i = _partitions.lower_bound(key, cache_entry::compare(_schema));
if (i == _partitions.end() || !i->key().equal(*_schema, key)) {
i = create_entry(i);
} else {
visit_entry(i);
}
if (!previous) {
return *i;
}
if ((!previous->_key && i == _partitions.begin())
|| (previous->_key && i != _partitions.begin()
&& std::prev(i)->key().equal(*_schema, *previous->_key))) {
i->set_continuous(true);
} else {
on_mispopulate();
}
return *i;
});
});
}
cache_entry& row_cache::find_or_create(const dht::decorated_key& key, tombstone t, row_cache::phase_type phase, const previous_entry_pointer* previous) {
return do_find_or_create_entry(key, previous, [&] (auto i) { // create
auto entry = current_allocator().construct<cache_entry>(cache_entry::incomplete_tag{}, _schema, key, t);
_tracker.insert(*entry);
return _partitions.insert(i, *entry);
}, [&] (auto i) { // visit
_tracker.on_miss_already_populated();
cache_entry& e = *i;
e.partition().open_version(*e.schema(), phase).partition().apply(t);
_tracker.touch(e);
upgrade_entry(e);
});
}
void row_cache::populate(const mutation& m, const previous_entry_pointer* previous) {
_populate_section(_tracker.region(), [&] {
do_find_or_create_entry(m.decorated_key(), previous, [&] (auto i) {
cache_entry* entry = current_allocator().construct<cache_entry>(
m.schema(), m.decorated_key(), m.partition());
upgrade_entry(*entry);
_tracker.insert(*entry);
entry->set_continuous(i->continuous());
return _partitions.insert(i, *entry);
}, [&] (auto i) {
throw std::runtime_error(sprint("cache already contains entry for {}", m.key()));
});
});
}
mutation_source& row_cache::snapshot_for_phase(phase_type phase) {
if (phase == _underlying_phase) {
return _underlying;
} else {
if (phase + 1 < _underlying_phase) {
throw std::runtime_error(sprint("attempted to read from retired phase {} (current={})", phase, _underlying_phase));
}
return *_prev_snapshot;
}
}
row_cache::snapshot_and_phase row_cache::snapshot_of(dht::ring_position_view pos) {
dht::ring_position_less_comparator less(*_schema);
if (!_prev_snapshot_pos || less(pos, *_prev_snapshot_pos)) {
return {_underlying, _underlying_phase};
}
return {*_prev_snapshot, _underlying_phase - 1};
}
void row_cache::invalidate_sync(memtable& m) noexcept {
with_allocator(_tracker.allocator(), [&m, this] () {
logalloc::reclaim_lock _(_tracker.region());
bool blow_cache = false;
// Note: clear_and_dispose() ought not to look up any keys, so it doesn't require
// with_linearized_managed_bytes(), but invalidate() does.
m.partitions.clear_and_dispose([this, deleter = current_deleter<memtable_entry>(), &blow_cache] (memtable_entry* entry) {
with_linearized_managed_bytes([&] {
try {
invalidate_locked(entry->key());
} catch (...) {
blow_cache = true;
}
deleter(entry);
});
});
if (blow_cache) {
// We failed to invalidate the key, presumably due to with_linearized_managed_bytes()
// running out of memory. Recover using clear_now(), which doesn't throw.
clear_now();
}
});
}
row_cache::phase_type row_cache::phase_of(dht::ring_position_view pos) {
dht::ring_position_less_comparator less(*_schema);
if (!_prev_snapshot_pos || less(pos, *_prev_snapshot_pos)) {
return _underlying_phase;
}
return _underlying_phase - 1;
}
template <typename Updater>
future<> row_cache::do_update(external_updater eu, memtable& m, Updater updater) {
return do_update(std::move(eu), [this, &m, updater = std::move(updater)] {
m.on_detach_from_region_group();
_tracker.region().merge(m); // Now all data in memtable belongs to cache
STAP_PROBE(scylla, row_cache_update_start);
auto cleanup = defer([&m, this] {
invalidate_sync(m);
STAP_PROBE(scylla, row_cache_update_end);
});
auto attr = seastar::thread_attributes();
attr.scheduling_group = &_update_thread_scheduling_group;
auto t = seastar::thread(attr, [this, &m, updater = std::move(updater)] () mutable {
// In case updater fails, we must bring the cache to consistency without deferring.
auto cleanup = defer([&m, this] {
invalidate_sync(m);
_prev_snapshot_pos = {};
_prev_snapshot = {};
});
partition_presence_checker is_present = _prev_snapshot->make_partition_presence_checker();
while (!m.partitions.empty()) {
with_allocator(_tracker.allocator(), [&] () {
unsigned quota = 30;
auto cmp = cache_entry::compare(_schema);
{
_update_section(_tracker.region(), [&] {
STAP_PROBE(scylla, row_cache_update_one_batch_start);
unsigned quota_before = quota;
// FIXME: we should really be checking should_yield() here instead of
// need_preempt() + quota. However, should_yield() is currently quite
// expensive and we need to amortize it somehow.
do {
auto i = m.partitions.begin();
STAP_PROBE(scylla, row_cache_update_partition_start);
with_linearized_managed_bytes([&] {
{
memtable_entry& mem_e = *i;
// FIXME: Optimize knowing we lookup in-order.
auto cache_i = _partitions.lower_bound(mem_e.key(), cmp);
updater(cache_i, mem_e, is_present);
i = m.partitions.erase(i);
current_allocator().destroy(&mem_e);
--quota;
}
});
STAP_PROBE(scylla, row_cache_update_partition_end);
} while (!m.partitions.empty() && quota && !need_preempt());
with_allocator(standard_allocator(), [&] {
if (m.partitions.empty()) {
_prev_snapshot_pos = {};
} else {
_prev_snapshot_pos = dht::ring_position(m.partitions.begin()->key());
}
});
STAP_PROBE1(scylla, row_cache_update_one_batch_end, quota_before - quota);
});
if (quota == 0 && seastar::thread::should_yield()) {
return;
}
}
});
seastar::thread::yield();
}
});
return do_with(std::move(t), [] (seastar::thread& t) {
return t.join();
}).then([cleanup = std::move(cleanup)] {});
});
}
future<> row_cache::update(external_updater eu, memtable& m) {
return do_update(std::move(eu), m, [this] (row_cache::partitions_type::iterator cache_i, memtable_entry& mem_e,
partition_presence_checker& is_present) mutable {
// If cache doesn't contain the entry we cannot insert it because the mutation may be incomplete.
// FIXME: keep a bitmap indicating which sstables we do cover, so we don't have to
// search it.
if (cache_i != partitions_end() && cache_i->key().equal(*_schema, mem_e.key())) {
cache_entry& entry = *cache_i;
upgrade_entry(entry);
entry.partition().apply_to_incomplete(*_schema, std::move(mem_e.partition()), *mem_e.schema());
_tracker.touch(entry);
_tracker.on_merge();
} else if (cache_i->continuous() || is_present(mem_e.key()) == partition_presence_checker_result::definitely_doesnt_exist) {
cache_entry* entry = current_allocator().construct<cache_entry>(
mem_e.schema(), std::move(mem_e.key()), std::move(mem_e.partition()));
entry->set_continuous(cache_i->continuous());
_tracker.insert(*entry);
_partitions.insert(cache_i, *entry);
}
});
}
future<> row_cache::update_invalidating(external_updater eu, memtable& m) {
return do_update(std::move(eu), m, [this] (row_cache::partitions_type::iterator cache_i, memtable_entry& mem_e,
partition_presence_checker& is_present) {
if (cache_i != partitions_end() && cache_i->key().equal(*_schema, mem_e.key())) {
// FIXME: Invalidate only affected row ranges.
// This invalidates all row ranges and the static row, leaving only the partition tombstone continuous,
// which has to always be continuous.
cache_entry& e = *cache_i;
e.partition() = partition_entry(mutation_partition::make_incomplete(*e.schema(), mem_e.partition().partition_tombstone()));
} else {
_tracker.clear_continuity(*cache_i);
}
});
}
void row_cache::refresh_snapshot() {
_underlying = _snapshot_source();
}
void row_cache::touch(const dht::decorated_key& dk) {
_read_section(_tracker.region(), [&] {
with_linearized_managed_bytes([&] {
auto i = _partitions.find(dk, cache_entry::compare(_schema));
if (i != _partitions.end()) {
_tracker.touch(*i);
}
});
});
}
void row_cache::invalidate_locked(const dht::decorated_key& dk) {
auto pos = _partitions.lower_bound(dk, cache_entry::compare(_schema));
if (pos == partitions_end() || !pos->key().equal(*_schema, dk)) {
_tracker.clear_continuity(*pos);
} else {
auto it = _partitions.erase_and_dispose(pos,
[this, &dk, deleter = current_deleter<cache_entry>()](auto&& p) mutable {
_tracker.on_erase();
deleter(p);
});
_tracker.clear_continuity(*it);
}
}
future<> row_cache::invalidate(external_updater eu, const dht::decorated_key& dk) {
return invalidate(std::move(eu), dht::partition_range::make_singular(dk));
}
future<> row_cache::invalidate(external_updater eu, const dht::partition_range& range) {
return invalidate(std::move(eu), dht::partition_range_vector({range}));
}
future<> row_cache::invalidate(external_updater eu, dht::partition_range_vector&& ranges) {
return do_update(std::move(eu), [this, ranges = std::move(ranges)] {
auto on_failure = defer([this] { this->clear_now(); });
with_linearized_managed_bytes([&] {
for (auto&& range : ranges) {
this->invalidate_unwrapped(range);
}
});
on_failure.cancel();
return make_ready_future<>();
});
}
void row_cache::evict(const dht::partition_range& range) {
invalidate_unwrapped(range);
}
void row_cache::invalidate_unwrapped(const dht::partition_range& range) {
logalloc::reclaim_lock _(_tracker.region());
auto cmp = cache_entry::compare(_schema);
auto begin = _partitions.lower_bound(dht::ring_position_view::for_range_start(range), cmp);
auto end = _partitions.lower_bound(dht::ring_position_view::for_range_end(range), cmp);
with_allocator(_tracker.allocator(), [this, begin, end] {
auto it = _partitions.erase_and_dispose(begin, end, [this, deleter = current_deleter<cache_entry>()] (auto&& p) mutable {
_tracker.on_erase();
deleter(p);
});
assert(it != _partitions.end());
_tracker.clear_continuity(*it);
});
}
row_cache::row_cache(schema_ptr s, snapshot_source src, cache_tracker& tracker, is_continuous cont)
: _tracker(tracker)
, _schema(std::move(s))
, _partitions(cache_entry::compare(_schema))
, _underlying(src())
, _snapshot_source(std::move(src))
{
with_allocator(_tracker.allocator(), [this, cont] {
cache_entry* entry = current_allocator().construct<cache_entry>(cache_entry::dummy_entry_tag());
_partitions.insert(*entry);
entry->set_continuous(bool(cont));
});
}
cache_entry::cache_entry(cache_entry&& o) noexcept
: _schema(std::move(o._schema))
, _key(std::move(o._key))
, _pe(std::move(o._pe))
, _flags(o._flags)
, _lru_link()
, _cache_link()
{
if (o._lru_link.is_linked()) {
auto prev = o._lru_link.prev_;
o._lru_link.unlink();
cache_tracker::lru_type::node_algorithms::link_after(prev, _lru_link.this_ptr());
}
{
using container_type = row_cache::partitions_type;
container_type::node_algorithms::replace_node(o._cache_link.this_ptr(), _cache_link.this_ptr());
container_type::node_algorithms::init(o._cache_link.this_ptr());
}
}
void row_cache::set_schema(schema_ptr new_schema) noexcept {
_schema = std::move(new_schema);
}
streamed_mutation cache_entry::read(row_cache& rc, read_context& reader) {
auto source_and_phase = rc.snapshot_of(_key);
reader.enter_partition(_key, source_and_phase.snapshot, source_and_phase.phase);
return do_read(rc, reader);
}
streamed_mutation cache_entry::read(row_cache& rc, read_context& reader,
streamed_mutation&& sm, row_cache::phase_type phase) {
reader.enter_partition(std::move(sm), phase);
return do_read(rc, reader);
}
// Assumes reader is in the corresponding partition
streamed_mutation cache_entry::do_read(row_cache& rc, read_context& reader) {
auto snp = _pe.read(_schema, reader.phase());
auto ckr = query::clustering_key_filter_ranges::get_ranges(*_schema, reader.slice(), _key.key());
auto sm = make_cache_streamed_mutation(_schema, _key, std::move(ckr), rc, reader.shared_from_this(), std::move(snp));
if (reader.schema()->version() != _schema->version()) {
sm = transform(std::move(sm), schema_upgrader(reader.schema()));
}
if (reader.fwd() == streamed_mutation::forwarding::yes) {
sm = make_forwardable(std::move(sm));
}
return std::move(sm);
}
const schema_ptr& row_cache::schema() const {
return _schema;
}
void row_cache::upgrade_entry(cache_entry& e) {
if (e._schema != _schema) {
auto& r = _tracker.region();
assert(!r.reclaiming_enabled());
with_allocator(r.allocator(), [this, &e] {
with_linearized_managed_bytes([&] {
e.partition().upgrade(e._schema, _schema);
e._schema = _schema;
});
});
}
}
std::ostream& operator<<(std::ostream& out, row_cache& rc) {
rc._read_section(rc._tracker.region(), [&] {
out << "{row_cache: " << ::join(", ", rc._partitions.begin(), rc._partitions.end()) << "}";
});
return out;
}
future<> row_cache::do_update(row_cache::external_updater eu, row_cache::internal_updater iu) noexcept {
return futurize_apply([this] {
return get_units(_update_sem, 1);
}).then([this, eu = std::move(eu), iu = std::move(iu)] (auto permit) mutable {
auto pos = dht::ring_position::min();
eu();
[&] () noexcept {
_prev_snapshot_pos = std::move(pos);
_prev_snapshot = std::exchange(_underlying, _snapshot_source());
++_underlying_phase;
}();
return futurize_apply([&iu] {
return iu();
}).then_wrapped([this, permit = std::move(permit)] (auto f) {
_prev_snapshot_pos = {};
_prev_snapshot = {};
if (f.failed()) {
clogger.warn("Failure during cache update: {}", f.get_exception());
}
});
});
}
std::ostream& operator<<(std::ostream& out, cache_entry& e) {
return out << "{cache_entry: " << e.position()
<< ", cont=" << e.continuous()
<< ", dummy=" << e.is_dummy_entry()
<< ", " << e.partition()
<< "}";
}
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