Summary

Capped collections can not be sharded. However, currently some suites that include the implicitly_shard_accessed_collections.js override do not exclude tests marked with the requires_capped tag. This makes tests using capped collections and correctly tagged as requires_capped to fail under those suites, unless additional tags such as assumes_unsharded_collection are also added.

Example

For example, the following simple test fails when executed under the fcv_upgrade_downgrade_sharded_collections_jscore_passthrough suite, as the suite does not exclude the requires_capped tag:

/**
 * @tags: [requires_capped]
 */

assert.commandWorked(db.createCollection("collection_capped", {
    capped: true,
    size: 1024,
}));
db.collection_capped.insertOne({a: 1});

Note however that some related suites such as sharded_collections_jscore_passthrough do in fact exclude the requires_capped tag.

Proposed solution

It would be sensible that all suites that include the implicitly_shard_accessed_collections.js override consistently exclude the requires_capped flag.

The way those suites deal with capped collections now is through manual excludes (example) and additional tags (example). Those can be removed once the requires_capped tag is enough to exclude them.

Additionally, some tests marked as requires_capped are able to complete successfully when running under implicitly sharded collection passthrough suites (for example, jstests/core/ddl/collation_convert_to_capped.js currently finishes successfully under the fcv_upgrade_downgrade_sharded_collections_jscore_passthrough suite). We should confirm that those tests are safe to exclude as they do not add additional coverage under those suites.