Optional per-tag materialized counters for archived messages.
Structure of tags_counters
tag_id
integer NOT NULL
The unique internal ID of the tag
REFERENCES
tags
cnt
integer
Partial count (a total count is obtained by adding all counts for a tag_id). May be negative to reflect untagging (only for entries with temp=false)
temp
boolean not null
True if that entry is meant to be summed up and merged into the corresponding non-temporary per-tag entry.