Transaction Operations

Redis transactions allow executing multiple commands at once, ensuring atomicity. Commands in a transaction are either all executed or none are executed.

Multi - Start Transaction

' Start transaction
oRedis.Multi

Exec - Commit Transaction

' Commit transaction and get execution results
Dim vResults As Variant
vResults = oRedis.Exec()

If IsArray(vResults) Then
    Dim i As Long
    For i = 0 To UBound(vResults)
        Debug.Print vResults(i)
    Next
End If

Discard - Cancel Transaction

' Cancel transaction
oRedis.Discard

Basic Usage

Simple Transaction Example

Sub SimpleTransaction()
    Dim oRedis As New cRedisClient

    If Not oRedis.Connect() Then
        Debug.Print "Connection failed: " & oRedis.LastError
        Exit Sub
    End If

    ' Start transaction
    oRedis.Multi

    ' Execute multiple commands (not executed immediately)
    oRedis.Set_ "key1", "value1"
    oRedis.Set_ "key2", "value2"
    oRedis.Incr "counter"

    ' Commit transaction
    Dim vResults As Variant
    vResults = oRedis.Exec()

    Debug.Print "Transaction execution results:"
    If IsArray(vResults) Then
        For i = 0 To UBound(vResults)
            Debug.Print "  Operation " & (i + 1) & " result: " & vResults(i)
        Next
    End If

    oRedis.DisConnect
End Sub

Use Cases

1. Atomic Counter

Sub AtomicCounter()
    Dim oRedis As New cRedisClient

    If Not oRedis.Connect() Then Exit Sub

    ' Initialize counter
    oRedis.Set_ "counter", "0"
    Debug.Print "Initial count: " & oRedis.Get_("counter")

    ' Start transaction
    oRedis.Multi

    ' Execute multiple increment operations
    oRedis.Incr "counter"
    oRedis.Incr "counter"
    oRedis.Incr "counter"

    ' Commit transaction
    Dim vResults As Variant
    vResults = oRedis.Exec()

    Debug.Print vbCrLf & "Transaction execution results:"
    If IsArray(vResults) Then
        For i = 0 To UBound(vResults)
            Debug.Print "  Operation " & (i + 1) & " result: " & vResults(i)
        Next
    End If

    Debug.Print "Final count: " & oRedis.Get_("counter")

    oRedis.DisConnect
End Sub

2. Bank Transfer

Sub BankTransfer()
    Dim oRedis As New cRedisClient

    If Not oRedis.Connect() Then Exit Sub

    ' Initialize account balances
    oRedis.Set_ "account:A", "1000"
    oRedis.Set_ "account:B", "500"

    Debug.Print "Before transfer:"
    Debug.Print "  Account A: " & oRedis.Get_("account:A")
    Debug.Print "  Account B: " & oRedis.Get_("account:B")

    Dim lAmount As Long
    lAmount = 200

    ' Start transaction
    oRedis.Multi

    ' Deduct from account A
    oRedis.DecrBy "account:A", lAmount

    ' Add to account B
    oRedis.IncrBy "account:B", lAmount

    ' Commit transaction
    Dim vResults As Variant
    vResults = oRedis.Exec()

    Debug.Print vbCrLf & "After transfer:"
    Debug.Print "  Account A: " & oRedis.Get_("account:A")
    Debug.Print "  Account B: " & oRedis.Get_("account:B")

    oRedis.DisConnect
End Sub

3. Batch Update

Sub BatchUpdate()
    Dim oRedis As New cRedisClient

    If Not oRedis.Connect() Then Exit Sub

    ' Start transaction
    oRedis.Multi

    ' Batch set multiple keys
    oRedis.Set_ "user:1", "Zhang San"
    oRedis.Set_ "user:2", "Li Si"
    oRedis.Set_ "user:3", "Wang Wu"
    oRedis.Set_ "user:4", "Zhao Liu"
    oRedis.Set_ "user:5", "Qian Qi"

    ' Batch set expiration times
    oRedis.Expire "user:1", 3600
    oRedis.Expire "user:2", 3600
    oRedis.Expire "user:3", 3600
    oRedis.Expire "user:4", 3600
    oRedis.Expire "user:5", 3600

    ' Commit transaction
    Dim vResults As Variant
    vResults = oRedis.Exec()

    Debug.Print "Batch update completed, executed " & (UBound(vResults) + 1) & " operations"

    oRedis.DisConnect
End Sub

4. Conditional Update

Sub ConditionalUpdate()
    Dim oRedis As New cRedisClient

    If Not oRedis.Connect() Then Exit Sub

    ' Initialize stock
    oRedis.Set_ "product:1001:stock", "10"
    Debug.Print "Initial stock: " & oRedis.Get_("product:1001:stock")

    Dim lBuyAmount As Long
    lBuyAmount = 3

    ' Check if stock is sufficient
    Dim lCurrentStock As Long
    lCurrentStock = CLng(oRedis.Get_("product:1001:stock"))

    If lCurrentStock >= lBuyAmount Then
        ' Stock sufficient, start transaction
        oRedis.Multi

        ' Reduce stock
        oRedis.DecrBy "product:1001:stock", lBuyAmount

        ' Increase sales
        oRedis.IncrBy "product:1001:sold", lBuyAmount

        ' Record sales log
        oRedis.RPush "sales:log", "Sold " & lBuyAmount & " items"

        ' Commit transaction
        Dim vResults As Variant
        vResults = oRedis.Exec()

        Debug.Print vbCrLf & "Purchase successful!"
        Debug.Print "Remaining stock: " & oRedis.Get_("product:1001:stock")
        Debug.Print "Total sold: " & oRedis.Get_("product:1001:sold")
    Else
        Debug.Print "Insufficient stock, cannot purchase"
    End If

    oRedis.DisConnect
End Sub

5. Data Consistency Check

Sub DataConsistency()
    Dim oRedis As New cRedisClient

    If Not oRedis.Connect() Then Exit Sub

    ' Initialize data
    oRedis.HSet "order:1001", "amount", "100"
    oRedis.HSet "order:1001", "status", "pending"
    oRedis.HSet "order:1001", "user", "user:123"

    oRedis.HSet "user:123", "balance", "500"

    ' Start transaction
    oRedis.Multi

    ' Get order amount
    oRedis.HGet "order:1001", "amount"

    ' Get user balance
    oRedis.HGet "user:123", "balance"

    ' Execute transaction to get data
    Dim vResults As Variant
    vResults = oRedis.Exec()

    ' Check if balance is sufficient
    If IsArray(vResults) And UBound(vResults) >= 1 Then
        Dim lOrderAmount As Long
        Dim lUserBalance As Long
        lOrderAmount = CLng(vResults(0))
        lUserBalance = CLng(vResults(1))

        If lUserBalance >= lOrderAmount Then
            ' Balance sufficient, execute payment
            oRedis.Multi

            ' Deduct user balance
            oRedis.HSet "user:123", "balance", CStr(lUserBalance - lOrderAmount)

            ' Update order status
            oRedis.HSet "order:1001", "status", "paid"

            ' Record payment log
            oRedis.RPush "payment:log", "Order 1001 payment " & lOrderAmount

            ' Commit transaction
            vResults = oRedis.Exec()

            Debug.Print "Payment successful"
            Debug.Print "Remaining balance: " & oRedis.HGet("user:123", "balance")
            Debug.Print "Order status: " & oRedis.HGet("order:1001", "status")
        Else
            Debug.Print "Insufficient balance, payment failed"
        End If
    End If

    oRedis.DisConnect
End Sub

6. Cancel Transaction

Sub CancelTransaction()
    Dim oRedis As New cRedisClient

    If Not oRedis.Connect() Then Exit Sub

    ' Initialize data
    oRedis.Set_ "counter", "10"
    Debug.Print "Initial value: " & oRedis.Get_("counter")

    ' Start transaction
    oRedis.Multi

    ' Execute multiple operations
    oRedis.Incr "counter"
    oRedis.Incr "counter"
    oRedis.Incr "counter"

    ' Cancel transaction
    oRedis.Discard

    Debug.Print "Value after canceling transaction: " & oRedis.Get_("counter")

    oRedis.DisConnect
End Sub

Transaction Features

1. Atomicity

Commands in a transaction are either all executed or none are executed:

Sub AtomicityExample()
    Dim oRedis As New cRedisClient

    If Not oRedis.Connect() Then Exit Sub

    oRedis.Multi

    ' These commands either all succeed or all fail
    oRedis.Set_ "key1", "value1"
    oRedis.Set_ "key2", "value2"
    oRedis.Set_ "key3", "value3"

    oRedis.Exec

    oRedis.DisConnect
End Sub

2. Isolation

During transaction execution, other clients cannot see intermediate states:

Sub IsolationExample()
    Dim oRedis As New cRedisClient

    If Not oRedis.Connect() Then Exit Sub

    ' Set initial value
    oRedis.Set_ "balance", "100"

    ' Start transaction
    oRedis.Multi

    ' Decrease balance (other clients still see 100 at this point)
    oRedis.Decr "balance"

    ' Can do other operations here...

    ' Commit transaction (other clients can now see changes)
    oRedis.Exec

    oRedis.DisConnect
End Sub

Notes

1. No Rollback: Redis transactions do not support rollback; even if a command fails, other commands will still be executed
2. Error Handling: Validate parameters before executing transaction
3. Performance Consideration: Transactions block other operations, avoid long-running transactions
4. Nested Transactions: Redis does not support nested transactions
5. Optimistic Locking: Can use WATCH command to implement optimistic locking (requires extended implementation)

Complete Example

Sub Example_Transaction()
    Dim oRedis As New cRedisClient

    If Not oRedis.Connect() Then
        Debug.Print "Connection failed: " & oRedis.LastError
        Exit Sub
    End If

    ' Initialize counter
    oRedis.Set_ "counter", "0"
    Debug.Print "Initial count: " & oRedis.Get_("counter")

    ' Start transaction
    oRedis.Multi

    ' Execute multiple increment operations
    oRedis.Incr "counter"
    oRedis.Incr "counter"
    oRedis.Incr "counter"

    ' Commit transaction
    Dim vResults As Variant
    vResults = oRedis.Exec()

    Debug.Print "Transaction execution results:"
    If IsArray(vResults) Then
        For i = 0 To UBound(vResults)
            Debug.Print "  Operation " & (i + 1) & " result: " & vResults(i)
        Next
    End If

    Debug.Print "Final count: " & oRedis.Get_("counter")

    oRedis.DisConnect
End Sub

Transaction vs Single Command

Scenario	Recommended Method	Reason
Single operation	Single command	Simple and direct
Multiple related ops	Transaction	Ensure atomicity
Unrelated operations	Single command	Reduce blocking
Need intermediate results	Step-by-step	More flexible
Batch update	Transaction or batch commands	Improve performance