Limits

Every limit has a default that suits a small team on one machine, and every one can be changed with an environment variable. The Configuration page lists them all.

Per statement

Limit	Default	Setting	Error
Run time of a query or batch	30 s	LUMBUNG_STATEMENT_TIMEOUT	statement_timeout
Rows one statement returns	10,000	LUMBUNG_MAX_RESULT_ROWS	result_too_large
Bytes one request returns	16 MiB	LUMBUNG_MAX_RESULT_BYTES	result_too_large
One string or blob	16 MiB	LUMBUNG_MAX_VALUE_BYTES	value_too_large
Statement text	1 MiB	LUMBUNG_MAX_SQL_BYTES	value_too_large
Bound parameters	10,000	LUMBUNG_MAX_PARAMS	sql_error
Memory per connection	128 MiB	LUMBUNG_CONN_MAX_MEMORY	memory_limit
Waiting for a lock	5 s	LUMBUNG_BUSY_TIMEOUT	busy

When a request hits a limit, nothing partial comes back and anything it wrote is rolled back. A statement cancelled by the timeout leaves its connection ready for the next request.

Storage

Limit	Default	Setting	Error
Size of one branch	1 GiB	LUMBUNG_MAX_BRANCH_BYTES	branch_size_limit (507)
Size of all branches together	10 GiB	LUMBUNG_MAX_INSTANCE_BYTES	instance_quota_exceeded (507)
Free disk before creating files	2 GiB	LUMBUNG_MIN_FREE_DISK	insufficient_disk (507)
Databases	100	LUMBUNG_MAX_DATABASES	limit_reached
Branches per database	50	LUMBUNG_MAX_BRANCHES	limit_reached

A full branch, or any branch on an instance at its quota, still serves reads and deletes, and writes that reuse the space deletes freed. SQLite doesn’t shrink a file when rows are deleted, so freed space is reused rather than returned.

The branch limit counts the database’s pages. The write-ahead log next to it is checkpointed and truncated once it passes a quarter of the branch limit (at most 1 MiB), so it stays small. The instance quota counts both, and a write may only claim half the free room in new pages, since each new page is written to the log first. Creating a branch, resetting one, importing and restoring a database from the trash are checked against the quota before they copy anything.

Connections

Each open branch has one writer connection and up to LUMBUNG_READERS_PER_BRANCH (4) read-only ones. Writes to one branch run one at a time; reads run alongside them. At most LUMBUNG_MAX_OPEN_BRANCHES (64) branches keep connections open; the least recently used idle one closes to make room, and any branch idle for LUMBUNG_IDLE_CONN_TIMEOUT (5 minutes) closes on its own. A closed branch reopens on the next request.