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Aug 14, 2025
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Document throughput based checkpoint limiter #2535

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Document throughput based checkpoint limiter
renetapopova Aug 14, 2025
e5a3e89
revert the unintentional removal of flush in the messages
renetapopova Aug 14, 2025
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19 changes: 18 additions & 1 deletion modules/ROOT/pages/database-internals/checkpointing.adoc
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Expand Up @@ -98,14 +98,31 @@ The default value of `db.tx_log.rotation.retention_policy` is changed from `2 da
For more information, see xref:database-internals/transaction-logs.adoc#transaction-logging-log-retention[Configure transaction log retention policy].

Having the least amount of transaction log data speeds up the checkpoint process.
To configure the number of IOs per second the checkpoint process is allowed to use, use the configuration parameter xref:configuration/configuration-settings.adoc#config_db.checkpoint.iops.limit[`db.checkpoint.iops.limit`].
To configure the number of IOs per second the checkpoint process is allowed to use, set the configuration parameter xref:configuration/configuration-settings.adoc#config_db.checkpoint.iops.limit[`db.checkpoint.iops.limit`].

[NOTE]
====
Disabling the IOPS limit can cause transaction processing to slow down a bit.
For more information, see xref:performance/disks-ram-and-other-tips.adoc#performance-checkpoint-iops-limit[Checkpoint IOPS limit] and xref:configuration/configuration-settings.adoc#_transaction_log_settings[Transaction log settings].
====

Additionally, starting from 2025.07, you can also use xref:configuration/configuration-settings.adoc#config_db.checkpoint.throughput.limit[`db.checkpoint.throughput.limit`] to define checkpoint speed in terms of bytes per second.
Compared to the IOPS limit, the throughput limit enforces a stricter control over flush speed, with the checkpoint process yielding more to stay within the configured throughput.

Starting from 2025.07, the checkpoint log messages also include the average flush speed:

.Example of a log message with IOPS-limited checkpoint
[results]
----
Checkpoint triggered by "Call to db.checkpoint() procedure" @ txId: 92, append index: 92 checkpoint completed in 7s 464ms. Checkpoint flushed 251909 pages (9% of total available pages), in 249641 IOs. Checkpoint performed with IO limit: 600 IOPS, paused in total 70 times(6026 millis). Average checkpoint flush speed: 281.1MiB/s.
----

.Example of a log message with throughput-limited checkpoint
[results]
----
Checkpoint triggered by "Call to db.checkpoint() procedure" @ txId: 88, append index: 88 checkpoint completed in 39s 457ms. Checkpoint flushed 314688 pages (12% of total available pages), in 311753 IOs. Checkpoint performed with IO limit: 64.00MiB/s, paused in total 77 times(38085 millis). Average checkpoint flush speed: 63.04MiB/s.
----

[[checkpoint-logging-and-metrics]]
== Checkpoint logging and metrics

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