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KAFKA-19151: docs: clarify that flush.ms requires log.flush.scheduler.interval.ms config #19479

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KAFKA-19151: docs: clarify that flush.ms requires log.flush.scheduler.interval.ms config #19479

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docs: enhance the docs of flush.ms by reminding users the flush is tr…
yunchipang Apr 15, 2025
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docs: replace double quotes with inline code; remove redundant explan…
yunchipang Apr 16, 2025
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6 changes: 4 additions & 2 deletions clients/src/main/java/org/apache/kafka/common/config/TopicConfig.java
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Original file line number Diff line number Diff line change
Expand Up @@ -58,8 +58,10 @@ public class TopicConfig {
public static final String FLUSH_MS_CONFIG = "flush.ms";
public static final String FLUSH_MS_DOC = "This setting allows specifying a time interval at which we will " +
"force an fsync of data written to the log. For example if this was set to 1000 " +
"we would fsync after 1000 ms had passed. In general we recommend you not set " +
"this and use replication for durability and allow the operating system's background " +
"we would fsync after 1000 ms had passed. Note that this setting depends on the broker-level " +
"configuration \"log.flush.scheduler.interval.ms\", which controls how frequently the flush check occurs. " +
"If \"log.flush.scheduler.interval.ms\" is not configured, the topic config \"flush.ms\" will not be triggered. " +
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nit: use <code></code> instead, so we can have code block for configuration.

Example:
Screenshot 2025-04-16 at 10 17 55 AM

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+1

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"If "log.flush.scheduler.interval.ms" is not configured, the topic config "flush.ms" will not be triggered. "

Maybe we can remove this as the remaining docs is good enough

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We can also use the LOG_FLUSH_SCHEDULER_INTERVAL_MS_CONFIG and FLUSH_MS_CONFIG constants instead of hardcoding the strings.

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@m1a2st The LOG_FLUSH_SCHEDULER_INTERVAL_MS_CONFIG is in org.apache.kafka.server.config.ServerLogConfigs. It already imported TopicConfig. I don't think we can import the ServerLogConfigs configuration in TopicConfig.

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The LOG_FLUSH_SCHEDULER_INTERVAL_MS_CONFIG is in org.apache.kafka.server.config.ServerLogConfigs

Thanks, but FLUSH_MS_CONFIG can update.

"In general we recommend you not set this and use replication for durability and allow the operating system's background " +
"flush capabilities as it is more efficient.";

public static final String RETENTION_BYTES_CONFIG = "retention.bytes";
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