johnjcasey commented on code in PR #28206:
URL: https://github.com/apache/beam/pull/28206#discussion_r1310757661
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sdks/java/core/src/main/java/org/apache/beam/sdk/io/FileIO.java:
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@@ -509,12 +509,22 @@ public MatchConfiguration
withEmptyMatchTreatment(EmptyMatchTreatment treatment)
* condition is reached, where the input to the condition is the
filepattern.
*
* <p>If {@code matchUpdatedFiles} is set, also watches for files with
timestamp change, with
- * the watching frequency given by the {@code interval}. The pipeline will
throw a {@code
- * RuntimeError} if timestamp extraction for the matched file has failed,
suggesting the
+ * the watching frequency given by the {@code interval}. The pipeline will
throw a
+ * {@code RuntimeError} if timestamp extraction for the matched file has
failed, suggesting the
* timestamp metadata is not available with the IO connector.
+ *
+ * <p>
+ * Matching continuously scales poorly, as it is stateful, and requires
storing file ids in
+ * memory. In addition, because it is memory-only, if a pipeline is
restarted, already processed
+ * files will be reprocessed. Consider an alternate technique, such as
+ * <a
href="https://cloud.google.com/storage/docs/pubsub-notifications";>Pub/Sub
Notifications</a>
+ * when using GCS if possible.
+ * </p>
*/
public MatchConfiguration continuously(
Duration interval, TerminationCondition<String, ?> condition, boolean
matchUpdatedFiles) {
+ LOG.warn("Matching Continuously is stateful, and can scale poorly.
Consider using Pub/Sub "
Review Comment:
will do
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