Progress of Cells Database schema migration work

Tables in main, (yet to be classified) - (272 tables, 43.31% of total)
Tables classified as main_clusterwide - (21 tables, 3.34% of total)
Tables classified as main_cell - (335 tables, 53.34% of total)

Total number of tables (does not include CI tables): 628

Outstanding cross-join issues

Number of cross-join issues to be fixed: 84

Outstanding cross-db foreign key issues

Number of cross-db foreign key issues to be fixed: 18

Number of tables over time

What does this graph signify?

This graph is used to assess how our "goal-post is moving" as new tables are being introduced

that does not belong to either the `gitlab_main_cell` or `gitlab_main_clusterwide` schema.

See this issue for details.

PS: This does not include CI tables.