Everything resumes with receipt of the thaw message.įor Master-Slave databases, the master is not affected. The database is still running but all requests will pause while the disks / file systems are synchronized. For a large database with GBs of memory that need to be flushed to disk, a number of seconds will be required.ĭuring the time that the freeze / thaw cycle is occurring, disk I/O for new user requests is suspended. Then the thaw (resume) message / command is sent to each application.įor a lightly used database this freeze / thaw process may take only a few hundred milliseconds. Once each application that supports snapshotting completes its preparation for freezing, the snaphot process then snaps the file systems, which means that if any further data blocks are written to, a copy is made first for the backup process (COW - Copy on Write). How long this flush takes depends on how much data is in memory, what state the data is in, and how long it takes to write the data to disk. The answer comes from understanding how snapshotting works.Īt the start of a snapshot, a message (command) is sent to all applications to come to a consistent state and flush necessary data to disk. What is general best practice to deal with these IO suspensions? As seems it happens even with automated backup, does it mean the site could possibly have a downtime everyday when DB snapshot creation is in progress? Automatic Backup creates a storage volume snapshot of your DB instance, backing up the entire DB instance and not just individual databases which provide. Which is not really clear how we can be sure if the DB instance I/O is functioning normally during snapshotting period, as if the DB is down for a short period we'd like to stop our corresponding web server or take it out of the load balancer to ensure no connection interruption could happen from customer side.ĭoes the DB really have downtime during snapshotting, AWS just says about "I/O suspension" and "latencies"? I read somewhere that the downtime lasts for short period (from few seconds to minute) just during snapshot initialization, can we know if that downtime has passed and the DB instance is ready to serve (while its snapshot still being created)? Providing Backups A Deployment, A Secret that contains information that is specific to the PostgreSQL cluster that it is deployed with (e.g. Minutes, depending on the size and class of your DB instance. According to AWS:Ĭreating this DB snapshot on a Single-AZ DB instance results in aīrief I/O suspension that can last from a few seconds to a few
Aws postgresql backup manual#
As we're relying on RDS Postgresql manual backup for our backup strategy, we encountered the issue with the possible downtime of the RDS instance (single AZ) during snapshot creation.
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