min_age_to_force_merge_on_partition_only and ReplacingMergeTree with is_deleted

[filimonov]

when min_age_to_force_merge_on_partition_only merge is happening it's actually safe to remove the rows with is_deleted flag from the target part (i.e. all the rows in partition are combined together, so no ghost rows can reappear if is_deleted for rows will be removed for the newer state - because it's guaranteed there that all parts from the begining of the partition are merged into a one).

[canhld94]

Looks not difficult to implement, but is is_deleted is still a thing? I thought the feature was removed before.

[aadant]

@canhld94 the feature is not removed. It is tricky to remove deleted rows if the data is not fully merged ... I have seen is_deleted on this recent project https://crypto.clickhouse.com/