Lesson Learned #436: Implementing Retry Mechanism with sqlcmd in Bash (Linux)

This post has been republished via RSS; it originally appeared at: Azure Database Support Blog articles.

Introduction:

Efficiently managing temporary failures and timeouts is crucial in production environments when connecting to databases. In this article, we’ll explore how to implement a retry mechanism with sqlcmd in a Bash script, dynamically increasing timeouts with each failed attempt.

 

Problem Statement:

Operations can fail due to network issues, overloaded servers, or other temporary problems when interacting with databases. Implementing a retry mechanism helps address these temporary issues without manual intervention.

 

Solution Overview:

Below is a Bash script utilizing sqlcmd to interact with an SQL Server database. The script attempts to execute an SQL command and, upon failure, retries the operation up to a maximum number of times, incrementing timeouts with each attempt.

 

 

 

 

#!/bin/bash # Variable declaration MAX_RETRIES=5 COUNT=0 SERVER="server.database.windows.net" DATABASE="dbname" USER="username" PASSWORD="Password123!" INPUT_FILE="/home/user/sql.sql" LOG_FILE="/home/user/logfile.txt" LOGIN_TIMEOUT=15 # Timeout for login, in seconds QUERY_TIMEOUT=30 # Timeout for query, in seconds # Main loop for retry mechanism while [ $COUNT -lt $MAX_RETRIES ]; do # Execute sqlcmd and capture the return value sqlcmd -S $SERVER -d $DATABASE -U $USER -P $PASSWORD -i $INPUT_FILE -l $LOGIN_TIMEOUT -t $QUERY_TIMEOUT 2>>$LOG_FILE RETVAL=$? # Get current date and time timestamp=$(date +"%Y-%m-%d %H:%M:%S") # Check the return value if [ $RETVAL -eq 0 ]; then message="$timestamp - sqlcmd executed successfully with login timeout $LOGIN_TIMEOUT and query timeout $QUERY_TIMEOUT!" echo $message echo $message >> $LOG_FILE break else message="$timestamp - Error with sqlcmd, retrying with increased timeouts..." echo $message echo $message >> $LOG_FILE # Increase timeouts by fixed amounts LOGIN_TIMEOUT=$((LOGIN_TIMEOUT + 15)) QUERY_TIMEOUT=$((QUERY_TIMEOUT + 30)) ((COUNT++)) # Wait for 5 seconds before retrying; adjust as needed sleep 5 fi done # Get current date and time timestamp=$(date +"%Y-%m-%d %H:%M:%S") # Check if the maximum number of attempts was reached if [ $COUNT -eq $MAX_RETRIES ]; then message="$timestamp - Failed after $MAX_RETRIES attempts with login timeout $LOGIN_TIMEOUT and query timeout $QUERY_TIMEOUT." echo $message echo $message >> $LOG_FILE fi

 

 

 

Script Explanation:

  • Variable Declaration: The script begins by declaring variables like the maximum number of retries, counter, server, database, user, password, input file, and timeouts.

  • Main Loop: A while loop serves as the main retry mechanism. The script runs sqlcmd and captures its return value.

  • Return Value Check: If sqlcmd executes successfully (return value 0), the script prints a success message and terminates. Otherwise, it prints an error message, increments timeouts and the retry counter, and sleeps for a while before retrying.

  • Timeout Increment: On each failed retry, login and query timeouts are increased by 15 and 30 seconds respectively, providing more time for subsequent operations.

 

Conclusion:

This Bash script is a valuable tool for managing database operations that might face temporary issues. With a retry mechanism and dynamically adjusted timeouts, you can enhance the robustness and reliability of your database interactions in unstable or high-load environments. We hope this article provided insightful information on effectively implementing a retry mechanism with sqlcmd in Bash. For optimal results, adjust variable values and timeouts to cater to your specific needs and production environment.

 

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