Logs are sent over network not instantly.

[alexey-milovidov]

Use case

When I do a query like

SELECT count() FROM merge('^text_log') WHERE pull_request_number = 63933 SETTINGS send_logs_level = 'trace'

The logs appear on the client, not as soon as they appear on the server. They are probably not flushed every time.

[azat]

The problem could be due to that some queries (i.e. SYSTEM/BACKUP/RESTORE) returns one block after everything is done, and so TCPHandler (clickhouse-server) do not poll for the logs in the mean time, only when new blocks arrived

[alexey-milovidov]

@azat It happens because the time is spent inside executeQuery, which is run in the foreground.
A solution could be - filter by secondary indices during query runtime instead of during planning.