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Limits Reference

This page documents the known limits of MuroDB. These limits arise from the fixed page size, serialization formats, and design decisions of the storage engine.

Page & Row Limits

LimitValueNotes
Page size4,096 bytesFixed; all data pages, B-tree nodes, and catalog entries use this size
Page header14 bytespage_id (8) + cell_count (2) + free_start (2) + free_end (2)
Max inline row size~4,073 bytesRows within this limit are stored inline in a single page
Max row size (with overflow)~4 GBLimited by u32 total_value_len; values exceeding inline limit use overflow pages
Max cell payload~4,073 bytes4,096 − 14 (header) − 5 (node header cell) − 4 (cell pointer + length prefix)
Overflow chunk size4,077 bytesPer overflow page: 4,096 − 19 bytes header

Rows with values that exceed the inline page capacity automatically use overflow pages. The value is stored in a chain of overflow pages, with the leaf cell containing only the key and a pointer to the first overflow page. Keys must still fit inline (max ~4,071 bytes).

Column Limits

LimitValueNotes
Max column count65,535 (u16)Serialization limit; practical limit is lower due to page capacity
Column name max length65,535 bytes (u16)Limited in practice by catalog page capacity
Table name max length65,535 bytes (u16)Limited in practice by catalog page capacity

Data Type Ranges

TypeMinMaxStorage
TINYINT−1281271 byte
SMALLINT−32,76832,7672 bytes
INT−2,147,483,6482,147,483,6474 bytes
BIGINT−2^632^63 − 18 bytes
FLOAT±1.2×10^−38±3.4×10^384 bytes (finite values only; NaN/Infinity rejected)
DOUBLE±2.2×10^−308±1.7×10^3088 bytes (finite values only; NaN/Infinity rejected)

String & Binary Limits

LimitValueNotes
VARCHAR(n) max n4,294,967,295 (u32)Values exceeding ~4,073 bytes use overflow pages
VARBINARY(n) max n4,294,967,295 (u32)Values exceeding ~4,073 bytes use overflow pages
TEXT max size~4 GBLimited by u32 value length; large values use overflow pages
VARCHAR(n) length checkCharacter-basedVARCHAR(100) allows up to 100 characters (MySQL-compatible)

Note: MuroDB checks VARCHAR(n) against character count, consistent with MySQL. Multi-byte UTF-8 characters (e.g., Japanese characters at 3 bytes each, emoji at 4 bytes) each count as one character. VARBINARY(n) still uses byte-based length checking.

Internal Limits

LimitValueNotes
B-tree max depth64Exceeded depth indicates corruption
WAL max frame length5,120 bytes
FTS inline segment limit3,000 bytesLarger posting lists use overflow pages
FTS max payload65,536 bytes
LRU cache default size256 pagesConfigurable

NULL Behavior

  • Primary key columns cannot be NULL
  • NULL = NULL evaluates to UNKNOWN (not TRUE); use IS NULL instead
  • Aggregate functions (SUM, AVG, MIN, MAX) skip NULL values
  • COUNT(*) counts all rows; COUNT(column) counts non-NULL values only
  • Multiple NULL values are allowed in UNIQUE indexes (SQL standard)
  • NULL values in ORDER BY are grouped together