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Add IStorage::totalBytes() interface

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This commit is contained in:
Azat Khuzhin 2020-03-29 11:38:38 +03:00
parent c2fbba7b9c
commit 4a7ee947b2
1 changed files with 20 additions and 2 deletions
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22
dbms/src/Storages/IStorage.h
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@ -459,13 +459,31 @@ public:
/// Returns storage policy if storage supports it
virtual StoragePolicyPtr getStoragePolicy() const { return {}; }
/** If it is possible to quickly determine exact number of rows in the table at this moment of time, then return it.
*/
/// If it is possible to quickly determine exact number of rows in the table at this moment of time, then return it.
/// Used for:
/// - Simple count() opimization
/// - For total_rows column in system.tables
///
/// Does takes underlying Storage (if any) into account.
virtual std::optional<UInt64> totalRows() const
{
return {};
}
/// If it is possible to quickly determine exact number of bytes for the table on storage:
/// - memory (approximated)
/// - disk (compressed)
///
/// Used for:
/// - For total_bytes column in system.tables
//
/// Does not takes underlying Storage (if any) into account
/// (since for Buffer we still need to know how much bytes it uses).
virtual std::optional<UInt64> totalBytes() const
{
return {};
}
private:
/// You always need to take the next three locks in this order.