This will fix race with DatabaseCatalog::loadMarkedAsDroppedTables(),
since MaterializeMySQL, and MaterializedMySQLSyncThread in background,
will be started earlier then
DatabaseCatalog::loadMarkedAsDroppedTables() and will move those tables
to metadata_dropped, and after loadMarkedAsDroppedTables() will start
and try to load partially dropped tables and will hit UUID overlap:
12:02:51.536783 [ 3026034 ] {} <Information> Application: starting up
12:02:53.019282 [ 3026034 ] {} <Information> DatabaseMaterializeMySQL<Atomic> (mysql): Total 9 tables and 0 dictionaries.
12:02:53.041699 [ 3026200 ] {} <Debug> mysql.data (7143b65f-6982-4600-b143-b65f6982e600): Loading data parts
12:02:53.041740 [ 3026200 ] {} <Debug> mysql.data (7143b65f-6982-4600-b143-b65f6982e600): There are no data parts
12:02:53.620382 [ 3026034 ] {} <Information> DatabaseMaterializeMySQL<Atomic> (mysql): Starting up tables.
12:03:00.669730 [ 3026183 ] {} <Debug> executeQuery: (internal) /*Materialize MySQL step 1: execute MySQL DDL for dump data*/ DROP TABLE mysql.data
12:03:00.741894 [ 3026269 ] {} <Information> DatabaseCatalog: Trying load partially dropped table mysql.data (7143b65f-6982-4600-b143-b65f6982e600) from /var/lib/clickhouse/metadata_dropped/mysql.data.7143b65f-6982-4600-b143-b65f6982e600.sql
12:03:00.742582 [ 3026269 ] {} <Debug> mysql.data (7143b65f-6982-4600-b143-b65f6982e600): Loading data parts
12:03:00.742650 [ 3026269 ] {} <Debug> mysql.data (7143b65f-6982-4600-b143-b65f6982e600): There are no data parts
12:03:00.773137 [ 3026034 ] {} <Error> Application: Caught exception while loading metadata: Code: 57, e.displayText() = DB::Exception: Mapping for table with UUID=7143b65f-6982-4600-b143-b65f6982e600 already exists. It happened due to UUID collision, most likely because some not random UUIDs were manually specified in CREATE queries., Stack trace (when copying this message, always include the lines below):
12:03:01.224557 [ 3026034 ] {} <Error> Application: DB::Exception: Mapping for table with UUID=7143b65f-6982-4600-b143-b65f6982e600 already exists. It happened due to UUID collision, most likely because some not random UUIDs were manually specified in CREATE queries.
Cc: @zhang2014
TODO (suggested by Nikolai)
1. Build query plan fro current query (inside storage::read) up to WithMergableState
2. Check, that plan is simple enough: Aggregating - Expression - Filter - ReadFromStorage (or simplier)
3. Check, that filter is the same as filter in projection, and also expression calculates the same aggregation keys as in projection
4. Return WithMergableState if projection applies
3 will be easier to do with ActionsDAG, cause it sees all functions, and dependencies are direct (but it is possible with ExpressionActions also)
Also need to figure out how prewhere works for projections, and
row_filter_policies.
wip
