Info

This test was introduced in SERVER-61158 to support collMod enhancements for indexes. The index spec is updated successfully in the index catalog but the WiredTiger storage engine fails on an invariant because the metadata changes, made with the the WT_SESSION::alter() function, did not go through as expected. We hit an invariant as we refresh the index using the WiredTigerUniqueIndex class.

Top User Comments

alexander.gorrod commented on Fri, 1 Dec 2023 02:42:40 +0000: Thanks yuhong.zhang@mongodb.com. steve.kuhn@mongodb.com could you please create a project titled "Altering table metadata without exclusive access in WiredTiger" (or similar), so we can get more specific about how much work would be involved on the WiredTiger side to support it, and find a way to get it scheduled. JIRAUSER1253424 commented on Thu, 16 Nov 2023 19:41:30 +0000: alexander.gorrod@mongodb.com alter is used by collMod which is a replicated command used to modify collection metadata. This can cause a problem when we have a replica set with a mix of nodes running in-memory and on-disk storage engine. Currently there is really not a good solution to this problem so we would like to check again if it's possible to fix alter for in-memory engine. alexander.gorrod commented on Wed, 25 Oct 2023 00:22:18 +0000: This is not simple to fix. The alter operation requires exclusive access to a data handle, which generally involves closing the handle and flushing associated content from the cache. It is not possible to do that when running with an in-memory only configuration, as the cache is the only place where the data exists. It should (on some level) be safe for the alter to proceed without needing exclusive access, since it does not need to be concerned about the durability of the change (there is no durability). It's quite a lot of work to add a different concurrency control mechanism to handle alter commands, and given that this has remained as-is for a fair while without user-complaint, I'm inclined to close it out. The engineering effort required isn't justified given the minimal end-user consequence. benety.goh@mongodb.com please re-open with additional context if this is the wrong decision. JIRAUSER1258229 commented on Mon, 13 Dec 2021 13:31:37 +0000: Error when running the repo: [js_test:collmod_convert_to_unique] [jsTest] ---- [js_test:collmod_convert_to_unique] [jsTest] Duplicate key error from failed conversion: { [js_test:collmod_convert_to_unique] [jsTest] "ok" : 0, [js_test:collmod_convert_to_unique] [jsTest] "errmsg" : "Failed to convert index to unique. firstRecordId: RecordId(1); firstDoc: { _id: 1.0, a: 100.0 }; secondRecordIdRecordId(2); secondDoc: { _id: 2.0, a: 100.0 }; collectionUUID: decc0ccf-78aa-426b-87ad-5037dabc61a8 :: caused by :: E11000 duplicate key error collection: test.collmod_convert_to_unique index: a_1 dup key: { a: 100.0 }", [js_test:collmod_convert_to_unique] [jsTest] "code" : 11000, [js_test:collmod_convert_to_unique] [jsTest] "codeName" : "DuplicateKey", [js_test:collmod_convert_to_unique] [jsTest] "keyPattern" : { [js_test:collmod_convert_to_unique] [jsTest] "a" : 1 [js_test:collmod_convert_to_unique] [jsTest] }, [js_test:collmod_convert_to_unique] [jsTest] "keyValue" : { [js_test:collmod_convert_to_unique] [jsTest] "a" : 100 [js_test:collmod_convert_to_unique] [jsTest] } [js_test:collmod_convert_to_unique] [jsTest] } [js_test:collmod_convert_to_unique] [jsTest] ---- I dug into the code and I found this ticket WT-3310 that introduces the following changes where an alter command is ignored in the in-memory configuration. This comment from agorrod suspected this code might need to be changed at some point. I removed those few lines from the code and the test runs successfully: /* In-memory ignores alter operations. */ - if (F_ISSET(S2C(session), WT_CONN_IN_MEMORY)) - goto err; + // if (F_ISSET(S2C(session), WT_CONN_IN_MEMORY)) + // goto err; It was a very quick investigation, we probably need to assess the impact(s) of allowing the alter command to be executed when WT is configured to be in memory. JIRAUSER1254368 commented on Thu, 25 Nov 2021 00:18:51 +0000: Scope: Investigate and create a WT ticket if there is a fix required at the WT end.

Steps to Reproduce