blob: 64443a3cfd6a8baf12e7e9be7ccea01faaf89dac (
plain) (
blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
|
#pragma once
#include <optional>
#include <Storages/IStorage.h>
namespace DB
{
/** Implements a table engine for the system table "zeros".
* The table contains the only column zero UInt8.
* From this table, you can read non-materialized zeros.
*
* You could also specify a limit (how many zeros to give).
* If multithreaded is specified, zeros will be generated in several streams.
*/
class StorageSystemZeros final : public IStorage
{
public:
/// If even_distribution is true, numbers are distributed evenly between streams.
/// Otherwise, streams concurrently increment atomic.
StorageSystemZeros(const StorageID & table_id_, bool multithreaded_, std::optional<UInt64> limit_ = std::nullopt);
std::string getName() const override { return "SystemZeros"; }
Pipe read(
const Names & column_names,
const StorageSnapshotPtr & storage_snapshot,
SelectQueryInfo & query_info,
ContextPtr context,
QueryProcessingStage::Enum processed_stage,
size_t max_block_size,
size_t num_streams) override;
bool hasEvenlyDistributedRead() const override { return true; }
bool isSystemStorage() const override { return true; }
bool supportsTransactions() const override { return true; }
private:
bool multithreaded;
std::optional<UInt64> limit;
};
}
|
