Setting value of a collection inserts tomstone

https://docs.datastax.com/en/landing_page/doc/landing_page/dataModel.html#dataModel__checkTableStructure

Check use of collection types

When insert or full update of a non-frozen collection occurs, such as replacing the value of the column with another value like UPDATE table SET field = new_value …, Cassandra inserts a tombstone marker to prevent possible overlap with previous data even if data did not previously exist. A large number of tombstones can significantly affect read performance.

When you know that no previous data exists and to prevent creation of tombstones when inserting data into a set or map (or when performing the full update of a set or map), you can use append operation for columns. For example:

CREATETABLE test.m1 (
id int PRIMARY KEY,
m map<int, text>
);

instead of using:

INSERT INTO test.m1(id, m) VALUES (1, {1:'t1', 2:'t2'}); 

or

UPDATE test.m1 SET m = {1:'t1', 2:'t2'} WHERE id = 1; 

which generate tombstones, execute:

UPDATE test.m1 SET m = m + {1:'t1', 2:'t2'} WHERE id = 1; 

which has the same result, but without tombstone generation.

Affected tables:

• imapUidTable (use of a non frozen set for user flags)
• inserts are done
• full updates are done
• This table is critical for JMAP performance. Not that it can explain the ~10% performance hit that occurs when reading mailbox with recent inserts versus reading mailboxes without recent inserts.

• messageIdTable (use of a non frozen set for user flags)
• inserts are done
• full updates are done
• This table is critical for IMAP performance.

• enqueuedMailsV3 (non frozen list data types are mistakenly used for RECIPIENTS and PER_RECIPIENT_SPECIFIC_HEADERS - frozen would be acceptable - map is used for attributed and could be frozen too)
• As a temporary measure, we can fix the inserts.
• This table is critical to the browse start update performance

• mailRepositoryContentV2 (non frozen list data types are mistakenly used for RECIPIENTS and PER_RECIPIENT_SPECIFIC_HEADERS - frozen would be acceptable- map is used for attributed and could be frozen too)
• As a temporary measure, we can fix the inserts.
• This table is not critical