Limits

KDBS has two kinds of limits: fixed limits built into the engine, and caps you set in the server config. A cap never silently truncates a result. Depending on the cap, the statement fails, the work falls back to a slower path that gives the same answer, or a value is not cached.

Identifiers and keys

Limit	Value	Config key	When exceeded
Primary-key id space, per table	[1, 2^48 - 1] = 1 to 281474976710655	none	A supplied key outside the range is refused OutOfRange with its byte position. When a table’s id space is used up, inserts are refused OutOfRange; ids never wrap. SHOW BUDGET warns at 90% used.
Issued-key redraws	8	none	An issued key that meets a concurrently supplied key 8 times in a row is refused AlreadyExists.
Primary-key column type	an integer type	none	Any other type is refused at CREATE TABLE. The id is stored in 48 bits whatever the declared width.
Cores	1 to 64, and not more than the machine reports	cores	The server refuses to start.
User columns, whole instance	about 7,800	none	CREATE TABLE is refused once the catalog’s reserved page range is full. DROP TABLE frees its column rows.

Rows per statement

Limit	Default	Config key	When exceeded
Rows in one INSERT ... VALUES	1024	max_insert_rows (at least 1)	The whole statement is refused and nothing is inserted: ERR INSERT of <n> rows exceeds max_insert_rows (<cap>).
Rows one statement may read	100,000,000	max_rows_touched (0 = unlimited)	The statement is refused ResourceExhausted, not retryable. Also bounds SHOW RELAYOUT <table>’s page census.
Rows one ORDER BY may hold	1,048,576	sort_max_rows	The statement fails, naming the key. There is no spill to disk and no partial result. A LIMIT caps what is held at offset + limit. ORDER BY <primary key> ascending needs no sort and is never limited.
Groups in one aggregated statement	65,536	aggregate_max_groups	The statement fails, naming the key. Nothing is returned.
DISTINCT entries in one statement, summed over its sets	1,048,576	aggregate_max_distinct	The statement fails, naming the key.
Rows in a join’s in-memory build	65,536	join_build_max_rows (0 = no build)	No error. The join falls back to per-row walks for the rest of the statement, with the same answer.
Lock-table entries per transaction	65,536	max_locks_per_txn	The statement is refused ResourceExhausted, not retryable. Use shorter transactions, or write by primary-key range, which takes one entry for the range.

Query shape

Limit	Value	When exceeded
ORDER BY keys	8	NOT_IMPLEMENTED with the byte position.
Subquery nesting below the outer query	4 levels	The fifth level is refused with its byte position.
Scalar subquery result	1 row	CardinalityViolation at run time, not retryable.
GROUP BY columns in an assertion	no cap

Values and columns

Limit	Value	When exceeded
Largest single value	8144 bytes (one var-heap page)	NotImplemented.
varchar cell width	inline_cell_width, default 64, range 16 to 4096	A value longer than width − 3 bytes is stored out of line; it is not refused below 8144 bytes.
varchar(N)	16 ≤ N ≤ 4096	N is a cell width, not a maximum length.
char(N)	N bytes	A longer value is refused. A value containing a NUL byte is refused.
decimal(p, s)	p ≤ 38; up to 18 is stored in 8 bytes, 19 to 38 in 16 bytes	Precision and scale are both required.
SUM	checked int64	Overflow fails the statement; it never wraps.
UPDATE arithmetic	checked in the result type	A result out of range is OutOfRange at that row; division by zero is InvalidArgument.

Indexes, Cabins and assertions

Limit	Default	Config key	When exceeded
Index key columns	4	none	NOT_IMPLEMENTED with the byte of the extra column.
Index covered columns	8	none	Refused with the byte of the extra column.
Cabin columns	1 per Cabin	none	A second column is refused.
Distinct values one Cabin observes	4096	cabin_max_values (0 = observe nothing)	The value is not observed and is served by a scan. Results are unchanged.
Entries per value in one Cabin	4096	cabin_max_entries_per_value	Same as above.
Pages for optimizer-managed Cabins	1024	cabin_optimizer_page_budget	The optimizer keeps the Cabins it manages within this budget.
Assertion bound	a non-negative integer literal	none	A negative or non-literal bound is refused. COUNT(*) <= 0 and < 1 are refused.

Time limits

Limit	Default	Config key	When exceeded
Explicit transaction lifetime	60,000 ms	txn_lifetime_ceiling_ms (0 refused)	The server rolls the transaction back. The next statement, COMMIT included, is refused RESOURCE_EXHAUSTED until the client sends ROLLBACK. Checked every quarter of the ceiling, so the rollback comes between 1× and 1.25× of it. Autocommit statements and bulk-load sessions are exempt. A running statement is never interrupted.
Wait before a lock wait is a fault	1000 ms	lock_wait_fault_net_ms (0 = refuse at once)	The waiting statement is aborted, never the holder, and the fault is logged. A normal wait ends earlier, when the holder commits or rolls back.
PURGE waiting for older readers	1 s	none	Refused TXN_CONFLICT retryable=1; nothing is purged.
relaxed commit loss window	10,000 µs	relaxed_flush_interval_us	Not an error; the commit is synced.
WAL drain cadence	1000 µs	wal_drain_interval_us	Not an error.
Checkpoint cadence	5000 ms	checkpoint_interval_ms	Not an error.
TCP keepalive idle	60 s, at most 32767	tcp_keepalive_s	A vanished client, or one that leaves a reply unread, is closed after about twice this.
Idle open backup	1 hour	none	The backup is aborted.

Memory and storage

Limit	Default	Config key	When exceeded
Buffer pool	required, no default	buffer_pool_frames (8 KiB frames)	A statement that needs more frames than the pool can free is refused ResourceExhausted. Below the floor (resident system and Bound Cabin pages plus 256 frames), the server refuses to mount.
WAL segment size	64 MiB	none (fixed per volume)
WAL archive fail-closed threshold	4 segments (256 MiB) free on the WAL filesystem	none	While archiving is failing, every statement that writes the log is refused. Reads continue.
Backup copy rate	up to 256 MiB/s	none

Protocol (KWP/1)

Limit	Value	When exceeded
Named statements per session	64	RESOURCE_EXHAUSTED, not retryable.
Portals per session	64	RESOURCE_EXHAUSTED, not retryable.
Frame length a client should accept	4 bytes to 16 MiB	Clients should refuse a frame length outside this range.

Related pages

• Server configuration: every key.
• Errors and refusals: the error each limit returns.
• Data types