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#pragma once
#include <Core/Types.h>
#include <Core/UUID.h>
#include <fmt/format.h>
#include <IO/WriteHelpers.h>
namespace DB
{
class IDataType;
using DataTypePtr = std::shared_ptr<const IDataType>;
class MergeTreeTransaction;
/// This macro is useful for places where a pointer to current transaction should be passed,
/// but transactions are not supported yet (e.g. when calling MergeTreeData's methods from StorageReplicatedMergeTree)
/// or transaction object is not needed and not passed intentionally.
#ifndef NO_TRANSACTION_PTR
#define NO_TRANSACTION_PTR std::shared_ptr<MergeTreeTransaction>(nullptr)
#define NO_TRANSACTION_RAW static_cast<MergeTreeTransaction *>(nullptr)
#endif
/// Commit Sequence Number
using CSN = UInt64;
/// Local part of TransactionID
using LocalTID = UInt64;
/// Hash of TransactionID that fits into 64-bit atomic
using TIDHash = UInt64;
namespace Tx
{
/// For transactions that are probably not committed (yet)
const CSN UnknownCSN = 0;
/// For changes were made without creating a transaction
const CSN PrehistoricCSN = 1;
/// Special reserved values
const CSN CommittingCSN = 2;
const CSN EverythingVisibleCSN = 3;
const CSN MaxReservedCSN = 32;
/// So far, that changes will never become visible
const CSN RolledBackCSN = std::numeric_limits<CSN>::max();
const LocalTID PrehistoricLocalTID = 1;
const LocalTID DummyLocalTID = 2;
const LocalTID MaxReservedLocalTID = 32;
}
struct TransactionID
{
/// Global sequential number, the newest commit timestamp the we saw when this transaction began
CSN start_csn = 0;
/// Local sequential that is unique for each transaction started by this host within specific start_csn
LocalTID local_tid = 0;
/// UUID of host that has started this transaction
UUID host_id = UUIDHelpers::Nil;
/// NOTE Maybe we could just generate UUIDv4 for each transaction, but it would be harder to debug.
/// Partial order is defined for this TransactionID structure:
/// (tid1.start_csn <= tid2.start_csn) <==> (tid1 <= tid2)
/// (tid1.start_csn == tid2.start_csn && tid1.host_id == tid2.host_id && tid1.local_tid < tid2.local_tid) ==> (tid1 < tid2)
/// If two transaction have the same start_csn, but were started by different hosts, then order is undefined.
bool operator == (const TransactionID & rhs) const
{
return start_csn == rhs.start_csn && local_tid == rhs.local_tid && host_id == rhs.host_id;
}
bool operator != (const TransactionID & rhs) const
{
return !(*this == rhs);
}
TIDHash getHash() const;
bool isEmpty() const
{
assert((local_tid == 0) == (start_csn == 0 && host_id == UUIDHelpers::Nil));
return local_tid == 0;
}
bool isPrehistoric() const
{
assert((local_tid == Tx::PrehistoricLocalTID) == (start_csn == Tx::PrehistoricCSN));
return local_tid == Tx::PrehistoricLocalTID;
}
static void write(const TransactionID & tid, WriteBuffer & buf);
static TransactionID read(ReadBuffer & buf);
};
namespace Tx
{
const TransactionID EmptyTID = {0, 0, UUIDHelpers::Nil};
const TransactionID PrehistoricTID = {PrehistoricCSN, PrehistoricLocalTID, UUIDHelpers::Nil};
const TransactionID DummyTID = {PrehistoricCSN, DummyLocalTID, UUIDHelpers::Nil};
}
}
template<>
struct fmt::formatter<DB::TransactionID>
{
template<typename ParseContext>
constexpr auto parse(ParseContext & context)
{
return context.begin();
}
template<typename FormatContext>
auto format(const DB::TransactionID & tid, FormatContext & context)
{
return fmt::format_to(context.out(), "({}, {}, {})", tid.start_csn, tid.local_tid, tid.host_id);
}
};
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