Slow & break MySQL operation

Started by islamicvashikaran, Oct 23, 2022, 09:48 AM

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islamicvashikaranTopic starter

What causes SQL to slow down and break connections? One possible reason is a high number of connections to the database, which can cause the CPU load to increase even though the CPU itself is not heavily loaded. This can result in exceptions such as "Timeout expired" or "Server not responding." MySQL version 8.0.35 is being used.

During normal operation, 300 clients create around 250-280 DB connections, but during the creation of new clients, this can increase to 1200-1700 DB connections. While the code seems fine, it's unclear why this happens. The requests executed when a client is created include creating a database, creating tables, and checking for and creating indexes.

It's possible these requests are causing the web server to become overloaded.

private void CreateDB()
        {
            try
            {
                using MySqlConnection Connect = DBUtils.GetDBConnection(_DbUserName, _DbPassword);
                Connect.Open();
                string SQL = $"CREATE DATABASE IF NOT EXISTS {_DbName} DEFAULT CHARACTER SET utf8mb4";
                using MySqlCommand command = new MySqlCommand(SQL, Connect);
                command.ExecuteNonQuery();
            }
            catch (Exception e)
            {
                _logWriter.LogWriterTask(e, "CreateTable()");
            }
        }
private void CreateTable()
        {
            try
            {
                using MySqlConnection Connect = DBUtils.GetDBConnection(_DbName, _DbUserName, _DbPassword);
                Connect.Open();
 
                string SQL = $"CREATE TABLE IF NOT EXISTS {_DbName}.dbUserTable ( dbID INTEGER NOT NULL AUTO_INCREMENT, TwitchID INTEGER NOT NULL UNIQUE, Name VARCHAR(30), " +
                "isSub INTEGER, isVip INTEGER, isMod INTEGER, IsBroadcaster INTEGER, UvalCon INTEGER, messageCon INTEGER, roulettCon INTEGER, roulettCD DOUBLE, UvalTimer DOUBLE, banCount INTEGER, Points DOUBLE, IsOnline INTEGER, PRIMARY KEY(dbID))";
                using (MySqlCommand Command = new MySqlCommand(SQL, Connect))
                {
                    Command.ExecuteNonQuery();
                }
 
                SQL = $"CREATE TABLE IF NOT EXISTS {_DbName}.dbUserMessageTable ( dbID INTEGER NOT NULL AUTO_INCREMENT, TwitchID INTEGER NOT NULL, Name VARCHAR(30), Message VARCHAR(600), TimeStamp DOUBLE, PRIMARY KEY(dbID))";
                using (MySqlCommand Command = new MySqlCommand(SQL, Connect))
                {
                    Command.ExecuteNonQuery();
                }
 
 
                SQL = $"SELECT COUNT(*) FROM INFORMATION_SCHEMA.STATISTICS WHERE table_schema = '{_DbName}' AND table_name = 'dbUserTable' AND index_name = 'index_Name'";
                int i = 0;
                using (MySqlCommand Command = new MySqlCommand(SQL, Connect))
                {
                    using var sqlReader = Command.ExecuteReader();
                    sqlReader.Read();
                    i = Convert.ToInt32(sqlReader[0]);
                }
                if (i == 0)
                {
                    SQL = $"CREATE UNIQUE INDEX index_Name ON {_DbName}.dbUserTable (Name)";
                    using var createIndexCmd = new MySqlCommand(SQL, Connect);
                    createIndexCmd.ExecuteNonQuery();
                }
            }
            catch (Exception e)
            {
                _logWriter.LogWriterTask(e, "CreateTable()");               
            }
        }

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patricka

Although I'm not an expert in databases, I suggest the following test: if your database and tables have the same name and categories each time a new client is created, pre-prepare them by creating everything in advance. Then, when a new client is created, you can focus only on the needed work, such as selecting or updating/inserting into an existing table.

Typically, one or two databases are sufficient for a task or project, with only 3-30 tables instead of 2000, which could confuse developers and cause other issues. In my opinion, your problem lies in the database architecture, but I must clarify that I am not an expert in this field and would rely on someone more knowledgeable to respond.
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cewarraph

There could be several reasons why SQL is slowing down and breaking connections in your case. Here are a few possibilities:

1. High number of connections: As mentioned earlier, a high number of connections can put a strain on the database server and cause it to slow down or become unresponsive. You mentioned that during the creation of new clients, the number of connections increases significantly. This sudden spike in connections could potentially overload the web server and impact its performance.

2. Resource limitations: Another possible reason for the slowdown could be resource limitations such as CPU, memory, or disk space. If the web server doesn't have enough resources to handle the increased workload, it can lead to performance issues and connection problems.

3. Inefficient queries or indexing: Poorly optimized SQL queries or missing/inefficient indexes can also contribute to slow performance. It's important to review the queries executed during client creation and ensure they are written efficiently. Additionally, check if all necessary indexes are in place to improve query performance.

4. Database configuration: The configuration settings of the MySQL database itself can also affect performance. Make sure the configuration parameters are set appropriately and optimize them based on the workload requirements.

5. Network issues: Connectivity problems or network bottlenecks can also cause SQL to slow down and break connections. Check for any network-related issues that might be impacting the communication between the web server and the database server.

additional steps you can take to further investigate and address the SQL slowdown and connection issues:

1. Check for locks and blocking: Long-running transactions or locks held by other queries can cause delays and block connections. Monitor for any locks, blocking, or contention in the database and identify the queries causing them. Optimizing those queries or adjusting transaction isolation levels can help mitigate the issue.

2. Review query execution plans: Examine the execution plans of the slow queries using EXPLAIN or equivalent tools. Look for any inefficiencies, such as full table scans or missing index usage. Optimizing the queries based on the execution plans can significantly improve performance.

3. Enable query and slow query logging: Enable query logging to capture the SQL statements executed against the database. This can provide insights into the frequency, duration, and performance of different queries. Additionally, enabling slow query logging can help identify queries that take a significant amount of time to execute, allowing you to focus on optimizing them.

4. Monitor database server metrics: Continuously monitor various performance metrics of your MySQL server, such as CPU usage, memory consumption, disk I/O, and network traffic. Identify any patterns or anomalies during periods of slowdown and correlate them with the connection issues. This can help pinpoint potential resource bottlenecks or abnormalities.

5. Consider scaling options: If the increased number of connections continues to overwhelm the web server, consider scaling your infrastructure. This could involve adding more web servers to distribute the load or upgrading the hardware resources of the existing server. You could also explore database-specific scaling options, such as sharding or clustering, to handle the increased workload.

6. Review MySQL configuration parameters: Ensure that the MySQL server is configured optimally for your workload. Review and adjust configuration parameters such as max_connections, innodb_buffer_pool_size, query_cache_size, and others based on the available system resources and workload requirements. Make sure the configuration aligns with the recommended best practices for your MySQL version.


Looking at the code snippet provided, I can see a couple of potential areas that might impact performance and connection stability:

1. Database connection management: Ensure that the database connections are being properly managed and closed after use. In both the `CreateDB()` and `CreateTable()` methods, it's important to explicitly close the database connections by calling `Connect.Close()` or using the `using` statement. Failure to close connections can result in resource leakage and eventually lead to connection issues.

2. Exception handling: While it's good to catch exceptions and log them, it's important to handle them appropriately. In the code snippet, exceptions caught in both the `CreateDB()` and `CreateTable()` methods are logged but not rethrown or handled further. Depending on the specific requirements and architecture of your application, consider whether additional error handling or exception propagation is necessary.

3. Resource utilization: The code creates indexes on tables and performs `SELECT` queries to check for existing indexes. Although this is a necessary step, depending on the size of the tables and the frequency at which this code is executed, it could potentially impact performance. Ensure that the database schema design and index creation operations are optimized for efficient execution.

4. Logging and error handling impact: The code logs exceptions or errors using `_logWriter.LogWriterTask()`. Depending on the implementation details of this logging mechanism, it's worth considering if the logging process itself could potentially impact performance and connections. Evaluate if any optimizations can be made to reduce the impact of logging on the overall system.

In summary, while the code snippet provided seems fine in terms of creating a database, creating tables, and checking/creating indexes, there are some considerations to keep in mind to ensure optimal performance and connection stability. Properly managing database connections, handling exceptions, optimizing resource utilization, and evaluating the impact of logging/error handling are key areas to focus on.
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