(superset) 01/01: docs(meta-db): warn that SUPERSET_META_DB_LIMIT truncates tables before joins

[ru...@apache.org]

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rusackas pushed a commit to branch docs/meta-db-join-limit-caveat
in repository https://gitbox.apache.org/repos/asf/superset.git

commit 2c63a838299e9a06b3f53f2b74d99e3cc4249e1b
Author: Evan <ev...@preset.io>
AuthorDate: Mon Jun 22 17:46:21 2026 -0700

    docs(meta-db): warn that SUPERSET_META_DB_LIMIT truncates tables before joins
    
    Addresses #36304. The Superset meta database applies SUPERSET_META_DB_LIMIT
    (default 1000) to each underlying table before the in-memory join runs, so a
    join over tables larger than the limit can silently return incomplete or empty
    results. Document this caveat near the existing SUPERSET_META_DB_LIMIT prose.
    
    Co-Authored-By: Claude Opus 4.8 <no...@anthropic.com>
---
 .../version-6.0.0/configuration/databases.mdx                         | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/docs/user_docs_versioned_docs/version-6.0.0/configuration/databases.mdx b/docs/user_docs_versioned_docs/version-6.0.0/configuration/databases.mdx
index 928856b2fed..779c33b05d1 100644
--- a/docs/user_docs_versioned_docs/version-6.0.0/configuration/databases.mdx
+++ b/docs/user_docs_versioned_docs/version-6.0.0/configuration/databases.mdx
@@ -1808,6 +1808,10 @@ If you enable DML in the meta database users will be able to run DML queries on
 
 Second, you might want to change the value of `SUPERSET_META_DB_LIMIT`. The default value is 1000, and defines how many are read from each database before any aggregations and joins are executed. You can also set this value `None` if you only have small tables.
 
+:::warning
+`SUPERSET_META_DB_LIMIT` is applied to **each** underlying table *before* the in-memory join runs, not to the final result. If any table involved in a join has more rows than the limit, the meta database will read only the first `SUPERSET_META_DB_LIMIT` rows of that table, which means matching rows can be silently dropped and the join can return **incomplete or even empty** results with no error. If you join tables larger than the limit, raise `SUPERSET_META_DB_LIMIT` to comfortably exce [...]
+:::
+
 Additionally, you might want to restrict the databases to with the meta database has access to. This can be done in the database configuration, under "Advanced" -> "Other" -> "ENGINE PARAMETERS" and adding:
 
 ```json