clickhouse online and offline table

1.background

I like to drop the table directly when I delete the table. When I recently encountered the drop table, the table was being written or other operations were performed, which caused the deletion of the table to fail.The operation is stopped, and then go to delete.

2. Description

Offline: DETACH TABLE|VIEW|DICTIONARY [IF EXISTS] [db.]name [ON CLUSTER cluster] [PERMANENTLY]
Online: ATTACH TABLE|VIEW|DICTIONARY [IF EXISTS] [db.]name [ON CLUSTER cluster] [PERMANENTLY]
Official website translation:

Detach does not delete data or metadata for tables, materialized views, or dictionaries.If an entity is not permanently detached, the next time the server starts, the server will read the metadata and recall the table/view/dictionary again.If an entity is permanently detached, there will be no automatic recall.Regardless of whether the table or dictionary is permanently detached, in both cases they can be reattached using an ATTACH query.System log tables can also be appended to the back (eg query_log, text_log, etc.).Unable to reconnect other system tables.At the next server startup, the server will recall these tables again.ATTACH materialized views cannot use short syntax (no SELECT), but it can be attached using an ATTACH TABLE query.Note that already detached tables (temporarily) cannot be detached permanently.But you can take it back and separate it permanently.You also cannot DROP the detached table, or use a CREATE table with the same name as the detached table, or replace it with another table with a RENAME table query.

3. Action

# test tableCREATE TABLE IF NOT EXISTS test.test_uid_20220803(`uid` Int32,`deviceId` String)ENGINE = ReplicatedMergeTree('/clickhouse/test/tables/{shard}/test_uid_20220803', '{replica}')PARTITION BY uidORDER BY uidSETTINGS index_granularity = 8192;# Test DataINSERT INTO test.test_uid_20220803SELECT 1, 'abcd';

# logout tabledetach table test.test_uid_20220803;# Querying again will show that the table does not existSELECT count()FROM test.test_uid_20220803Received exception from server (version 21.3.15):Code: 60. DB::Exception: Received from 127.0.0.1:9000. DB::Exception: Table test.test_uid_20220803 doesn't exist.# Temporarily the table structure still exists, but it is hidden by ck and goes online againattach table test.test_uid_20220803;# delete tabledrop table test.test_uid_20220803;

Reference documentation: clickhouse official documentation