It's calculated by the seconds_behind_master metric that's available in MySQL. This metric is available only on read replica servers. The SQL thread reads the relay log and then applies the data changes on replica servers.Īzure Database for MySQL provides the metric for replication lag in seconds in Azure Monitor.Those updates are saved on a replica server, in a local log called the relay log. This thread receives the binary log updates. The IO thread connects to the source server and requests updated binary logs.One thread is the IO thread, and the other is the SQL thread: On replica servers, two threads run on each replica server. It's turned on by default for all newly provisioned servers that support up to 16 TB of storage. When a binary log is enabled, the source server writes committed transactions into the binary log. When the term is removed from the software, we'll remove it from this article. This article contains references to the term slave, a term that Microsoft no longer uses. You'll also understand some common causes of increased replication latency on replica servers.
#MYSQL UUID PRIMARY KEY DEFAULT HOW TO#
In this article, you learn how to troubleshoot replication latency in Azure Database for MySQL. Queries running on the source server and secondary server.Compute tier of the source server and secondary read replica server.Transaction volume on the source server.These factors include but aren't limited to: The replication lag on the secondary read replicas depends several factors. For more information, see MySQL binlog file position-based replication configuration overview. Replicas are updated asynchronously by using the MySQL engine's native binary log (binlog) file position-based replication technology. It also improves overall performance and latency of the application as it scales. This setup reduces the pressure on the source server. You can scale out workloads by routing read and reporting queries from the application to replica servers. The read replica feature allows you to replicate data from an Azure Database for MySQL server to a read-only replica server. seems like bikeshedding, but, whatever.This article references the term slave, which Microsoft no longer uses. If you want to transform them to something other than the standard format for UI reasons, that doesn’t preclude using UUIDs in the DB. Just “don’t use a clustered index where distributed key generation is important” seems a better rule, even if it precludes MySQL/InnoDB use.Īlso, most DB’s that explicitly handle UUIDs store them compactly as 128-bit values. > You can still use a unique identifier alongside an incrementing primary key, and you could choose to use a more compact format than the UUID.Ī key point of using a UUID is distributed generation avoiding lock contention on a sequence generator, which is defeated by using both. PG doesn't have clustered indexes at all, DB2 has a thing called clustered indexes which aren’t quite the same thing, Oracle calls having a clustered index on the PK an “index organized table” and its an non-default table option, and SQLite has what seems equivalent to a clustered index ONLY for INTEGER PRIMARY KEY tables not declared as WITHOUT ROWID. Can't speak for all dbs, but many use a clustered index on the primary key.ĪFAIK, only MySQL (with InnoDB engine) and SQL Server, AFAIK, do it by default (always for MySQL/InnoDB, and by default unless you create a different clustered index before adding the PK constraint for SQL Server, but even then you can specify a nonclustered PK index.)
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