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rocksdb: trivial count

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Signed-off-by: Duc Canh Le <duccanh.le@ahrefs.com>
This commit is contained in:
Duc Canh Le 2023-10-19 04:03:08 +00:00
parent 70711b0898
commit b708fa21f9
5 changed files with 25 additions and 0 deletions
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1
src/Core/Settings.h
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@ -546,6 +546,7 @@ class IColumn;
M(Bool, database_atomic_wait_for_drop_and_detach_synchronously, false, "When executing DROP or DETACH TABLE in Atomic database, wait for table data to be finally dropped or detached.", 0) \
M(Bool, enable_scalar_subquery_optimization, true, "If it is set to true, prevent scalar subqueries from (de)serializing large scalar values and possibly avoid running the same subquery more than once.", 0) \
M(Bool, optimize_trivial_count_query, true, "Process trivial 'SELECT count() FROM table' query from metadata.", 0) \
M(Bool, rocksdb_enable_approximate_count, true, "If `optimize_trivial_count_query` is true, process trivial 'SELECT count() FROM rockdb_table' from metadata, the returned result is approximated.", 0) \
M(Bool, optimize_count_from_files, true, "Optimize counting rows from files in supported input formats", 0) \
M(Bool, use_cache_for_count_from_files, true, "Use cache to count the number of rows in files", 0) \
M(Bool, optimize_respect_aliases, true, "If it is set to true, it will respect aliases in WHERE/GROUP BY/ORDER BY, that will help with partition pruning/secondary indexes/optimize_aggregation_in_order/optimize_read_in_order/optimize_trivial_count", 0) \

14
src/Storages/RocksDB/StorageEmbeddedRocksDB.cpp
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@ -609,5 +609,19 @@ void registerStorageEmbeddedRocksDB(StorageFactory & factory)
factory.registerStorage("EmbeddedRocksDB", create, features);
}
std::optional<UInt64> StorageEmbeddedRocksDB::totalRows(const Settings & settings) const
{
if (settings.rocksdb_enable_approximate_count)
{
std::shared_lock lock(rocksdb_ptr_mx);
if (!rocksdb_ptr)
return {};
UInt64 estimated_rows;
if (!rocksdb_ptr->GetIntProperty("rocksdb.estimate-num-keys", &estimated_rows))
return {};
return estimated_rows;
}
return {};
}
}

4
src/Storages/RocksDB/StorageEmbeddedRocksDB.h
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@ -83,6 +83,10 @@ public:
bool supportsDelete() const override { return true; }
bool supportsTrivialCountOptimization() const override { return true; }
std::optional<UInt64> totalRows(const Settings & settings) const override;
private:
const String primary_key;
using RocksDBPtr = std::unique_ptr<rocksdb::DB>;

2
tests/queries/0_stateless/02892_rocksdb_trivial_count.reference Normal file
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@ -0,0 +1,2 @@
121
121

4
tests/queries/0_stateless/02892_rocksdb_trivial_count.sql Normal file
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@ -0,0 +1,4 @@
CREATE TABLE dict (key UInt64, value String) ENGINE = EmbeddedRocksDB PRIMARY KEY key;
INSERT INTO dict SELECT number, toString(number) FROM numbers(121);
SELECT count() FROM dict SETTINGS rocksdb_enable_approximate_count = 0;
SELECT count() FROM dict SETTINGS optimize_trivial_count_query = 1, rocksdb_enable_approximate_count = 1;