clarified modules;

renamed object Data to private_data, to emphasize its intended scope (but it is publicly accessible in the database);

more conservative build_delay (despite 9600720071e6): avoid exessive build_database operations, notably via ssh;

proper running limit, based on this worker process; prefer bulk jobs: much faster cancellation;

more robust: implicit locking of tables in standard order;

more uniform guard (!exists_table(table)): avoid "ALTER TABLE" on already existing table, which could lead to deadlocks if this is presently locked;

removed unused "create_index": implicit index from primary_key is usually sufficient;

clarified "vacuum" (again, reverting 0bd366fad888);

clarified signature: eliminate SQL.Tables.empty to avoid confusion (see also 0bd366fad888);

update for release;

merged

more elementary transaction implementation (despite fda3f7a158b9 and 9da65bc75610);

tuned signature;

proper check (amending 234f2ff9afe6);

more robust: exclude accidental nesting (synchronized block is re-entrant);

clarified errors;

removed junk (amending f8e3b228670c);

tuned output;

reuse SSH.Server connection for database server;

tuned source structure;

clarified check: uniform session_info_exists;

more complete check;

clarified signature: more specific exists_table --- avoid retrieving full list beforehand;

reuse database_server connection;

more informative trace;

reuse SSH.Server connection database server;

tuned output;

make double-sure that this is a transaction context, notably for LOCK TABLE;

more robust Java/Scala multithreading: transaction is always connection.synchronized;

clarified signature: proper Scala function for command-line tool;