Files
scylla/data_dictionary/data_dictionary.cc
Benny Halevy c5668d99c9 schema: add per-table tablet options
Unlike with vnodes, each tablet is served only by a single
shard, and it is associated with a memtable that, when
flushed, it creates sstables which token-range is confined
to the tablet owning them.

On one hand, this allows for far better agility and elasticity
since migration of tablets between nodes or shards does not
require rewriting most if not all of the sstables, as required
with vnodes (at the cleanup phase).

Having too few tablets might limit performance due not
being served by all shards or by imbalance between shards
caused by quantization.  The number of tabelts per table has to be
a power of 2 with the current design, and when divided by the
number of shards, some shards will serve N tablets, while others
may serve N+1, and when N is small N+1/N may be significantly
larger than 1. For example, with N=1, some shards will serve
2 tablet replicas and some will serve only 1, causing an imbalance
of 100%.

Now, simply allocating a lot more tablets for each table may
theoretically address this problem, but practically:
a. Each tablet has memory overhead and having too many tablets
in the system with many tables and many tablets for each of them
may overwhelm the system's and cause out-of-memory errors.
b. Too-small tablets cause a proliferation of small sstables
that are less efficient to acces, have higher metadata overhead
(due to per-sstable overhead), and might exhaust the system's
open file-descriptors limitations.

The options introduced in this change can help the user tune
the system in two ways:
1. Sizing the table to prevent unnecessary tablet splits
and migrations.  This can be done when the table is created,
or later on, using ALTER TABLE.
2. Controlling min_per_shard_tablet_count to improve
tablet balancing, for hot tables.

Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
2025-02-06 08:55:51 +02:00

489 lines
16 KiB
C++

/*
* Copyright (C) 2021-present ScyllaDB
*/
/*
* SPDX-License-Identifier: LicenseRef-ScyllaDB-Source-Available-1.0
*/
#include <ranges>
#include "data_dictionary.hh"
#include "cql3/description.hh"
#include "impl.hh"
#include "user_types_metadata.hh"
#include "keyspace_metadata.hh"
#include "schema/schema.hh"
#include "cql3/util.hh"
#include "gms/feature_service.hh"
#include <fmt/core.h>
#include <fmt/ranges.h>
#include <fmt/std.h>
#include <ios>
#include <ostream>
#include <array>
#include "replica/database.hh"
namespace data_dictionary {
schema_ptr
table::schema() const {
return _ops->get_table_schema(*this);
}
const std::vector<view_ptr>&
table::views() const {
return _ops->get_table_views(*this);
}
const secondary_index::secondary_index_manager&
table::get_index_manager() const {
return _ops->get_index_manager(*this);
}
lw_shared_ptr<keyspace_metadata>
keyspace::metadata() const {
return _ops->get_keyspace_metadata(*this);
}
const user_types_metadata&
keyspace::user_types() const {
return metadata()->user_types();
}
bool
keyspace::is_internal() const {
return _ops->is_internal(*this);
}
bool
keyspace::uses_tablets() const {
return metadata()->uses_tablets();
}
const locator::abstract_replication_strategy&
keyspace::get_replication_strategy() const {
return _ops->get_replication_strategy(*this);
}
const table_schema_version&
database::get_version() const {
return _ops->get_version(*this);
}
std::optional<keyspace>
database::try_find_keyspace(std::string_view name) const {
return _ops->try_find_keyspace(*this, name);
}
bool
database::has_keyspace(std::string_view name) const {
return bool(try_find_keyspace(name));
}
keyspace
database::find_keyspace(std::string_view name) const {
auto ks = try_find_keyspace(name);
if (!ks) {
throw no_such_keyspace(name);
}
return *ks;
}
std::vector<keyspace>
database::get_keyspaces() const {
return _ops->get_keyspaces(*this);
}
std::vector<sstring>
database::get_user_keyspaces() const {
return _ops->get_user_keyspaces(*this);
}
std::vector<sstring>
database::get_all_keyspaces() const {
return _ops->get_all_keyspaces(*this);
}
std::vector<table>
database::get_tables() const {
return _ops->get_tables(*this);
}
std::optional<table>
database::try_find_table(std::string_view ks, std::string_view table) const {
return _ops->try_find_table(*this, ks, table);
}
table
database::find_table(std::string_view ks, std::string_view table) const {
auto t = try_find_table(ks, table);
if (!t) {
throw no_such_column_family(ks, table);
}
return *t;
}
std::optional<table>
database::try_find_table(table_id id) const {
return _ops->try_find_table(*this, id);
}
table
database::find_column_family(table_id uuid) const {
auto t = try_find_table(uuid);
if (!t) {
throw no_such_column_family(uuid);
}
return *t;
}
schema_ptr
database::find_schema(std::string_view ks, std::string_view table) const {
return find_table(ks, table).schema();
}
schema_ptr
database::find_schema(table_id uuid) const {
return find_column_family(uuid).schema();
}
bool
database::has_schema(std::string_view ks_name, std::string_view cf_name) const {
return bool(try_find_table(ks_name, cf_name));
}
table
database::find_column_family(schema_ptr s) const {
return find_column_family(s->id());
}
schema_ptr
database::find_indexed_table(std::string_view ks_name, std::string_view index_name) const {
return _ops->find_indexed_table(*this, ks_name, index_name);
}
sstring
database::get_available_index_name(std::string_view ks_name, std::string_view table_name,
std::optional<sstring> index_name_root) const {
return _ops->get_available_index_name(*this, ks_name, table_name, index_name_root);
}
std::set<sstring>
database::existing_index_names(std::string_view ks_name, std::string_view cf_to_exclude) const {
return _ops->existing_index_names(*this, ks_name, cf_to_exclude);
}
schema_ptr
database::get_cdc_base_table(std::string_view ks_name, std::string_view table_name) const {
return get_cdc_base_table(*find_table(ks_name, table_name).schema());
}
schema_ptr
database::get_cdc_base_table(const schema& s) const {
return _ops->get_cdc_base_table(*this, s);
}
const db::extensions&
database::extensions() const {
return _ops->get_extensions(*this);
}
const gms::feature_service&
database::features() const {
return _ops->get_features(*this);
}
const db::config&
database::get_config() const {
return _ops->get_config(*this);
}
replica::database&
database::real_database() const {
return _ops->real_database(*this);
}
replica::database* database::real_database_ptr() const {
return _ops->real_database_ptr(*this);
}
impl::~impl() = default;
keyspace_metadata::keyspace_metadata(std::string_view name,
std::string_view strategy_name,
locator::replication_strategy_config_options strategy_options,
std::optional<unsigned> initial_tablets,
bool durable_writes,
std::vector<schema_ptr> cf_defs,
user_types_metadata user_types,
storage_options storage_opts)
: _name{name}
, _strategy_name{locator::abstract_replication_strategy::to_qualified_class_name(strategy_name.empty() ? "NetworkTopologyStrategy" : strategy_name)}
, _strategy_options{std::move(strategy_options)}
, _initial_tablets(initial_tablets)
, _durable_writes{durable_writes}
, _user_types{std::move(user_types)}
, _storage_options(make_lw_shared<storage_options>(std::move(storage_opts)))
{
for (auto&& s : cf_defs) {
_cf_meta_data.emplace(s->cf_name(), s);
}
}
void keyspace_metadata::validate(const gms::feature_service& fs, const locator::topology& topology) const {
using namespace locator;
locator::replication_strategy_params params(strategy_options(), initial_tablets());
auto strategy = locator::abstract_replication_strategy::create_replication_strategy(strategy_name(), params);
strategy->validate_options(fs, topology);
}
lw_shared_ptr<keyspace_metadata>
keyspace_metadata::new_keyspace(std::string_view name,
std::string_view strategy_name,
locator::replication_strategy_config_options options,
std::optional<unsigned> initial_tablets,
bool durables_writes,
storage_options storage_opts,
std::vector<schema_ptr> cf_defs)
{
return ::make_lw_shared<keyspace_metadata>(name, strategy_name, options, initial_tablets, durables_writes, cf_defs, user_types_metadata{}, storage_opts);
}
lw_shared_ptr<keyspace_metadata>
keyspace_metadata::new_keyspace(const keyspace_metadata& ksm) {
return new_keyspace(ksm.name(), ksm.strategy_name(), ksm.strategy_options(), ksm.initial_tablets(), ksm.durable_writes(), ksm.get_storage_options());
}
void keyspace_metadata::add_user_type(const user_type ut) {
_user_types.add_type(ut);
}
void keyspace_metadata::remove_user_type(const user_type ut) {
_user_types.remove_type(ut);
}
std::vector<schema_ptr> keyspace_metadata::tables() const {
return _cf_meta_data
| std::views::values
| std::views::filter([] (const auto& s) { return !s->is_view(); })
| std::ranges::to<std::vector<schema_ptr>>();
}
std::vector<view_ptr> keyspace_metadata::views() const {
return _cf_meta_data
| std::views::values
| std::views::filter([] (const auto& s) { return s->is_view(); })
| std::views::transform([] (auto& s) { return view_ptr(s); })
| std::ranges::to<std::vector<view_ptr>>();
}
storage_options::local storage_options::local::from_map(const std::map<sstring, sstring>& values) {
if (!values.empty()) {
throw std::runtime_error("Local storage does not accept any custom options");
}
return {};
}
std::map<sstring, sstring> storage_options::local::to_map() const {
return {};
}
storage_options::s3 storage_options::s3::from_map(const std::map<sstring, sstring>& values) {
s3 options;
const std::array<std::pair<sstring, sstring*>, 2> allowed_options {
std::make_pair("bucket", &options.bucket),
std::make_pair("endpoint", &options.endpoint),
};
for (auto& option : allowed_options) {
if (auto it = values.find(option.first); it != values.end()) {
*option.second = it->second;
} else {
throw std::runtime_error(fmt::format("Missing S3 option: {}", option.first));
}
}
if (values.size() > allowed_options.size()) {
throw std::runtime_error(fmt::format("Extraneous options for S3: {}; allowed: {}",
fmt::join(values | std::views::keys, ","),
fmt::join(allowed_options | std::views::keys, ",")));
}
return options;
}
std::map<sstring, sstring> storage_options::s3::to_map() const {
return {{"bucket", bucket},
{"endpoint", endpoint}};
}
bool storage_options::is_local_type() const noexcept {
return std::holds_alternative<local>(value);
}
storage_options::value_type storage_options::from_map(std::string_view type, std::map<sstring, sstring> values) {
if (type == local::name) {
return local::from_map(values);
}
if (type == s3::name) {
return s3::from_map(values);
}
throw std::runtime_error(fmt::format("Unknown storage type: {}", type));
}
std::string_view storage_options::type_string() const {
return std::visit([] (auto& opt) { return opt.name; }, value);
}
std::map<sstring, sstring> storage_options::to_map() const {
return std::visit([] (auto& opt) { return opt.to_map(); }, value);
}
bool storage_options::can_update_to(const storage_options& new_options) {
return value == new_options.value;
}
storage_options storage_options::append_to_s3_prefix(const sstring& s) const {
// when restoring from object storage, the API of /storage_service/restore
// provides:
// 1. a shared prefix
// 2. a list of sstables, each of which has its own partial path
//
// for example, assuming we have following API call:
// - shared prefix: /bucket/ks/cf
// - sstables
// - 3123/me-3gdq_0bki_2cvk01yl83nj0tp5gh-big-TOC.txt
// - 3123/me-3gdq_0bki_2edkg2vx4xtksugjj5-big-TOC.txt
// - 3245/me-3gdq_0bki_2cvk02wubgncy8qd41-big-TOC.txt
//
// note, this example shows three sstables from two different snapshot backups.
//
// we assume all sstables' locations share the same base prefix (storage_options::s3::prefix).
// however, sstable in different backups have different prefixes. to handle this, we compose
// a per-sstable prefix by concatenating the shared prefix and the "parent directory" of the
// sstable's location. the resulting structure looks like:
//
// sstables:
// - prefix: /bucket/ks/cf/3123
// desc: me-3gdq_0bki_2cvk01yl83nj0tp5gh-big
// - prefix: /bucket/ks/cf/3123
// desc: me-3gdq_0bki_2edkg2vx4xtksugjj5-big
// - prefix: /bucket/ks/cf/3145
// desc: me-3gdq_0bki_2cvk02wubgncy8qd41-big
SCYLLA_ASSERT(!is_local_type());
storage_options ret = *this;
if (s.empty()) {
// scylla-manager should always pass sstables with non-empty dirname,
// but still..
return ret;
}
s3 s3_options = std::get<s3>(value);
SCYLLA_ASSERT(std::holds_alternative<sstring>(s3_options.location));
sstring prefix = std::get<sstring>(s3_options.location);
s3_options.location = seastar::format("{}/{}", prefix, s);
ret.value = std::move(s3_options);
return ret;
}
no_such_keyspace::no_such_keyspace(std::string_view ks_name)
: runtime_error{fmt::format("Can't find a keyspace {}", ks_name)}
{
}
no_such_column_family::no_such_column_family(const table_id& uuid)
: runtime_error{fmt::format("Can't find a column family with UUID {}", uuid)}
{
}
no_such_column_family::no_such_column_family(std::string_view ks_name, std::string_view cf_name)
: runtime_error{fmt::format("Can't find a column family {} in keyspace {}", cf_name, ks_name)}
{
}
no_such_column_family::no_such_column_family(std::string_view ks_name, const table_id& uuid)
: runtime_error{fmt::format("Can't find a column family with UUID {} in keyspace {}", uuid, ks_name)}
{
}
cql3::description keyspace_metadata::describe(const replica::database& db, cql3::with_create_statement with_create_statement) const {
auto maybe_create_statement = std::invoke([&] -> std::optional<sstring> {
if (!with_create_statement) {
return std::nullopt;
}
std::ostringstream os;
os << "CREATE KEYSPACE " << cql3::util::maybe_quote(_name)
<< " WITH replication = {'class': " << cql3::util::single_quote(_strategy_name);
for (const auto& opt: _strategy_options) {
os << ", " << cql3::util::single_quote(opt.first) << ": " << cql3::util::single_quote(opt.second);
}
if (!_storage_options->is_local_type()) {
os << "} AND storage = {'type': " << cql3::util::single_quote(sstring(_storage_options->type_string()));
for (const auto& e : _storage_options->to_map()) {
os << ", " << cql3::util::single_quote(e.first) << ": " << cql3::util::single_quote(e.second);
}
}
os << "} AND durable_writes = " << std::boolalpha << _durable_writes << std::noboolalpha;
if (db.features().tablets) {
if (!_initial_tablets.has_value()) {
os << " AND tablets = {'enabled': false}";
} else if (_initial_tablets.value() > 0) {
os << " AND tablets = {'initial': " << _initial_tablets.value() << "}";
} else {
os << " AND tablets = {'enabled': true}";
}
}
os << ";";
return std::move(os).str();
});
return cql3::description {
.keyspace = name(),
.type = "keyspace",
.name = name(),
.create_statement = std::move(maybe_create_statement)
};
}
} // namespace data_dictionary
template <>
struct fmt::formatter<data_dictionary::user_types_metadata> {
constexpr auto parse(format_parse_context& ctx) { return ctx.begin(); }
auto format(const data_dictionary::user_types_metadata& m, fmt::format_context& ctx) const
-> decltype(ctx.out()) {
return fmt::format_to(ctx.out(),
"org.apache.cassandra.config.UTMetaData@{}",
fmt::ptr(&m));
}
};
auto fmt::formatter<data_dictionary::keyspace_metadata>::format(const data_dictionary::keyspace_metadata& m, fmt::format_context& ctx) const -> decltype(ctx.out()) {
fmt::format_to(ctx.out(), "KSMetaData{{name={}, strategyClass={}, strategyOptions={}, cfMetaData={}, durable_writes={}, tablets=",
m.name(), m.strategy_name(), m.strategy_options(), m.cf_meta_data(), m.durable_writes());
if (m.initial_tablets()) {
fmt::format_to(ctx.out(), "{{\"initial\":{}}}", m.initial_tablets().value());
} else {
fmt::format_to(ctx.out(), "{{\"enabled\":false}}");
}
return fmt::format_to(ctx.out(), ", userTypes={}}}", m.user_types());
}
auto fmt::formatter<data_dictionary::storage_options>::format(const data_dictionary::storage_options& so, fmt::format_context& ctx) const -> decltype(ctx.out()) {
return std::visit(overloaded_functor {
[&ctx] (const data_dictionary::storage_options::local& so) -> decltype(ctx.out()) {
return fmt::format_to(ctx.out(), "{}", so.dir);
},
[&ctx] (const data_dictionary::storage_options::s3& so) -> decltype(ctx.out()) {
return std::visit(overloaded_functor {
[&ctx, &so] (const sstring& prefix) -> decltype(ctx.out()) {
return fmt::format_to(ctx.out(), "s3://{}/{}", so.bucket, prefix);
},
[&ctx, &so] (const table_id& owner) -> decltype(ctx.out()) {
return fmt::format_to(ctx.out(), "s3://{} (owner {})", so.bucket, owner);
}
}, so.location);
}
}, so.value);
}