diff --git a/information-schema/information-schema-partitions.md b/information-schema/information-schema-partitions.md
index 61510949922ab..bbb98ad0fe567 100644
--- a/information-schema/information-schema-partitions.md
+++ b/information-schema/information-schema-partitions.md
@@ -7,6 +7,10 @@ summary: Learn the `PARTITIONS` INFORMATION_SCHEMA table.
 
 The `PARTITIONS` table provides information about [partitioned tables](/partitioned-table.md).
 
+> **Note:**
+>
+> Computing `AVG_ROW_LENGTH`, `DATA_LENGTH`, or `INDEX_LENGTH` requires TiDB to read per-column size statistics from the `mysql.stats_histograms` system table, which holds one row for each column of every table. On clusters with a large number of tables, selecting any of these columns can consume noticeably more time and resources than selecting only `TABLE_ROWS`, which reads only the smaller `mysql.stats_meta` system table. If you need only the estimated row count, select `TABLE_ROWS` without the size columns to avoid this overhead.
+
 ```sql
 USE INFORMATION_SCHEMA;
 DESC partitions;
diff --git a/information-schema/information-schema-tables.md b/information-schema/information-schema-tables.md
index 77eb125c82bde..0bf33f43caf4f 100644
--- a/information-schema/information-schema-tables.md
+++ b/information-schema/information-schema-tables.md
@@ -123,6 +123,10 @@ The description of columns in the `TABLES` table is as follows:
 * `CREATE_OPTIONS`: Creates options.
 * `TABLE_COMMENT`: The comments and notes of the table.
 
+> **Note:**
+>
+> Computing `AVG_ROW_LENGTH`, `DATA_LENGTH`, or `INDEX_LENGTH` requires TiDB to read per-column size statistics from the `mysql.stats_histograms` system table, which holds one row for each column of every table. On clusters with a large number of tables, selecting any of these columns can consume noticeably more time and resources than selecting only `TABLE_ROWS`, which reads only the smaller `mysql.stats_meta` system table. If you need only the estimated row count, select `TABLE_ROWS` without the size columns to avoid this overhead.
+
 Most of the information in the table is the same as MySQL. The following columns are newly defined by TiDB:
 
 * `TIDB_TABLE_ID`: to indicate the internal ID of a table. This ID is unique in a TiDB cluster.