yuqi1129 commented on code in PR #10383:
URL: https://github.com/apache/gravitino/pull/10383#discussion_r2964776902
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catalogs-contrib/catalog-jdbc-clickhouse/src/main/java/org/apache/gravitino/catalog/clickhouse/operations/ClickHouseClusterUtils.java:
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@@ -36,11 +36,60 @@
* <li>{@code system.databases.cluster} is only populated for {@code
Replicated}-engine databases.
* </ul>
*
- * <p>Gravitino therefore embeds the cluster name inside the object's COMMENT
field at creation time
- * using a non-printable SOH separator ({@code \u0001}). The metadata is
invisible to end users
- * because Gravitino strips it before surfacing the comment.
+ * <p>Gravitino therefore embeds the cluster name inside the object's COMMENT
field at creation
+ * time, separated from the user comment by a newline. The metadata line is
always stripped before
+ * surfacing the comment to callers.
*
- * <p><b>Stored format:</b> {@code userComment\u0001ch.cluster=clusterName}
+ * <p><b>Stored format:</b>
+ *
+ * <pre>userComment
+ * [Gravitino] ch.cluster=clusterName</pre>
+ *
+ * <p><b>Example — database created ON CLUSTER:</b>
+ *
+ * <pre>
+ * -- Gravitino issues:
+ * CREATE DATABASE `my_db` ON CLUSTER `ck_cluster`
+ * COMMENT 'my comment\n[Gravitino] ch.cluster=ck_cluster'
+ *
+ * -- ClickHouse SHOW CREATE DATABASE output (ON CLUSTER is omitted):
+ * CREATE DATABASE my_db
+ * ENGINE = Atomic
+ * COMMENT 'my comment
+ * [Gravitino] ch.cluster=ck_cluster'
+ *
+ * -- Gravitino reads back from system.databases.comment:
+ * -- stored : 'my comment\n[Gravitino] ch.cluster=ck_cluster'
+ * -- cluster: 'ck_cluster' (extracted by extractClusterFromComment)
+ * -- user : 'my comment' (stripped by stripClusterMetadata)
+ * </pre>
+ *
+ * <p><b>Example — table created ON CLUSTER:</b>
+ *
+ * <pre>
+ * -- Gravitino issues:
+ * CREATE TABLE `orders` ON CLUSTER `ck_cluster`
+ * (`id` Int32, `amount` Decimal(10,2))
+ * ENGINE = MergeTree()
+ * ORDER BY `id`
+ * COMMENT 'order records\n[Gravitino] ch.cluster=ck_cluster'
+ *
Review Comment:
Do you mean users will update the comment without using Gravitino and add
something at the end of `\n[Gravitino] ch.cluster=ck_cluster`?
We can't avoid such a problem as long as users can update comments without
notifying Gravitino.
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