cqlite-py 0.14.0

Python bindings for CQLite - read Cassandra 5.0 SSTables locally without a cluster

cqlite-py

Python bindings for CQLite - a high-performance library for reading Apache Cassandra 5.0 SSTable files locally, without requiring a running Cassandra cluster.

Installation

pip install cqlite-py

Quick Start

import cqlite

# Open a database with schema
with cqlite.open('path/to/sstables', schema='schema.cql') as db:
    # Execute queries
    for row in db.execute('SELECT * FROM keyspace.table LIMIT 10'):
        print(row.to_dict())

Features

• Zero cluster dependency - Read SSTable files directly from disk
• Full CQL type support - All primitive types, collections, UDTs, and frozen types
• Memory-efficient streaming - Iterate over large datasets without loading all rows
• Thread-safe database handles - Safe concurrent access from multiple threads
• Cross-platform - Linux (x86_64, ARM64), macOS (Intel, Apple Silicon), Windows

Supported Platforms

Platform	Architecture	Status
Linux	x86_64	✅
Linux	ARM64	✅
macOS	Intel (x86_64)	✅
macOS	Apple Silicon	✅
Windows	x64	✅

Requirements

• Python 3.9+
• Cassandra 5.0 SSTable files

API Reference

Opening a Database

import cqlite

# Context manager (recommended)
with cqlite.open(data_dir, schema=schema_path) as db:
    # use db...

# Manual management
db = cqlite.open(data_dir, schema=schema_path)
# use db...
db.close()

Executing Queries

# Simple query
results = db.execute('SELECT * FROM keyspace.table')
for row in results:
    print(row.to_dict())

# With LIMIT
for row in db.execute('SELECT name, age FROM users LIMIT 100'):
    print(f"{row['name']}: {row['age']}")

# Access query metadata
print(f"Rows returned: {len(results)}")
print(f"Execution time: {results.execution_time_ms}ms")
print(f"Columns: {[col.name for col in results.columns]}")

Streaming Large Results

For memory-efficient iteration over large datasets:

from cqlite import StreamingConfig

# Configure streaming for memory efficiency
config = StreamingConfig(buffer_size=512, chunk_size=1000)
for row in db.execute_streaming('SELECT * FROM large_table', config=config):
    process(row)

# Track progress
iterator = db.execute_streaming('SELECT * FROM large_table')
for row in iterator:
    if iterator.rows_received % 10000 == 0:
        print(f"Processed {iterator.rows_received} rows")

Configuration Presets

import cqlite

# Built-in presets for common use cases
config = cqlite.memory_optimized()      # 256 MB max memory
config = cqlite.performance_optimized() # 4 GB max memory

# Open database with preset configuration
db = cqlite.open('path/to/data', schema='schema.cql', config='memory_optimized')

# Validate custom configuration
custom_config = {'memory': {'max_memory': 536870912}}  # 512 MB
cqlite.validate_config(custom_config)

Refreshing SSTables (v0.13)

If Cassandra (or another process) writes new SSTables while your database handle is open, call refresh() to re-discover them. Refresh is explicit-only (CQLite never rescans behind your back) and atomic / fail-closed: if any newly found generation fails to open, the swap is rolled back and the handle keeps serving the prior, consistent set of readers.

import cqlite

with cqlite.open('path/to/sstables', schema='schema.cql') as db:
    # ... time passes; Cassandra flushes/compacts new SSTables to disk ...

    report = db.refresh()
    print(f'Tables scanned:  {report.tables_scanned}')
    print(f'Readers added:   {report.readers_added}')
    print(f'Readers removed: {report.readers_removed}')

    # Subsequent queries see the newly discovered data
    for row in db.execute('SELECT * FROM keyspace.table'):
        print(row.to_dict())

refresh() returns a RefreshReport with the integer attributes tables_scanned, readers_added, and readers_removed, plus a to_dict() helper. It raises RuntimeError if the database is already closed, and CqliteError if a newly discovered generation fails to open (the prior reader set is preserved).

Result Byte Budget (v0.13)

Non-streaming execute() queries are bounded by a result-size budget, defaulting to 64 MiB (64 * 1024 * 1024 bytes). When the materialized result's running byte estimate exceeds the budget, the query fails with a cqlite.QueryError directing you to add a LIMIT clause or switch to execute_streaming(). Streaming queries are not subject to this budget.

Adjust the budget with the max_result_bytes key in the config passed to cqlite.open() (absent, it stays at 64 MiB):

import cqlite

# Raise the budget to 256 MiB for this handle
config = {'max_result_bytes': 256 * 1024 * 1024}

try:
    with cqlite.open('path/to/data', schema='schema.cql', config=config) as db:
        rows = db.execute('SELECT * FROM keyspace.big_table')
        for row in rows:
            process(row)
except cqlite.QueryError as e:
    # Result exceeded the byte budget — add a LIMIT or stream instead
    print(f'Result too large: {e}')
    for row in db.execute_streaming('SELECT * FROM keyspace.big_table'):
        process(row)

OpenTelemetry Tracing (v0.13)

CQLite can emit OpenTelemetry traces when built with the observability Cargo feature; without that feature the configuration is accepted but is a no-op. Pass an otel_config dict to cqlite.open(). Values are layered over the CQLITE_OTEL_* environment variables, and OpenTelemetry is initialized once per process.

import cqlite

db = cqlite.open(
    'path/to/sstables',
    schema='schema.cql',
    otel_config={
        'enabled': True,                       # default False
        'endpoint': 'http://localhost:4317',   # default 'http://localhost:4317'
        'protocol': 'grpc',                    # 'grpc' (default) or 'http'
        'service_name': 'cqlite',              # default 'cqlite'
        'service_version': '0.13.0',           # default: package version
        'sampling_ratio': 1.0,                 # default 1.0
        'timeout_ms': 10000,                   # default 10000
    },
)

Unknown keys raise ValueError.

Error Handling

import cqlite

try:
    with cqlite.open('path/to/data', schema='schema.cql') as db:
        result = db.execute('SELECT * FROM keyspace.table')
        for row in result:
            print(row.to_dict())
except cqlite.ParseError as e:
    print(f"Query syntax error: {e}")
except cqlite.QueryError as e:
    print(f"Query execution failed: {e}")
except cqlite.SchemaError as e:
    print(f"Schema validation failed: {e}")
except IOError as e:
    print(f"File not found: {e}")
except RuntimeError as e:
    print(f"Database already closed: {e}")

Exception Hierarchy:

CqliteError (base exception)
├── SchemaError   - Schema parsing or validation failures
├── QueryError    - Query execution failures
└── ParseError    - CQL syntax errors

Built-in exceptions also used:
├── IOError       - File system errors
├── ValueError    - Invalid configuration
├── RuntimeError  - Invalid state (e.g., database closed)
└── MemoryError   - Memory allocation failures

Type Conversions

CQL types are automatically converted to Python native types:

CQL Type	Python Type
text, varchar	str
int, bigint, smallint, tinyint	int
float, double	float
boolean	bool
blob	bytes
timestamp	datetime.datetime
date	datetime.date
time	int (nanoseconds since midnight, lossless)
duration	cqlite.Duration (exact months / days / nanos)
uuid, timeuuid	uuid.UUID
inet	ipaddress.IPv4Address or IPv6Address
decimal	decimal.Decimal
varint	int (arbitrary precision)
list<T>	list
set<T>	frozenset
map<K,V>	dict
tuple<...>	tuple
frozen<T>	Unwrapped inner type
UDT	dict with _type and _keyspace keys

Write Operations

CQLite v0.9.0 adds write support to the Python bindings. Open the database with writable=True and a write_dir to enable write operations.

import cqlite

with cqlite.open(
    'path/to/sstables',
    schema='schema.cql',
    writable=True,
    write_dir='/tmp/my-writes',
) as db:
    # Write rows via CQL INSERT, UPDATE, or DELETE
    db.execute(
        "INSERT INTO test_basic.simple_table (id, name, age) "
        "VALUES (11111111-1111-1111-1111-111111111111, 'Alice', 30)"
    )
    db.execute(
        "UPDATE test_basic.simple_table SET age = 31 "
        "WHERE id = 11111111-1111-1111-1111-111111111111"
    )

    # Flush the in-memory write buffer (memtable) to an SSTable on disk.
    # Returns the path to the flushed Data.db file.
    path = db.flush_run()
    print(f'Flushed to: {path}')

    # Run background compaction within a time budget
    report = db.maintenance_step(budget_ms=100)
    print(f'Merged {report.rows_merged} rows in {report.time_spent_ms:.1f} ms')
    if report.pending_compaction:
        print('More compaction work available')

    # Inspect write statistics
    stats = db.write_stats
    print(f'Memtable size: {stats.memtable_size_bytes} bytes')
    print(f'Total flushed: {stats.total_written_bytes} bytes')

Write API

Method / Property	Description
db.execute(cql)	Execute a CQL INSERT, UPDATE, or DELETE statement
db.flush_run()	Flush memtable to SSTable; returns the Data.db path or "" if memtable was empty
db.maintenance_step(budget_ms)	Run STCS compaction for up to budget_ms milliseconds; returns MaintenanceReport
db.write_stats	WriteStats property: memtable_size_bytes, memtable_row_count, total_written_bytes, l0_sstable_count

Known Limitations

• Counter columns cannot be written — execute() raises CqliteError for counter mutations.
• Concurrent queries on the same handle may need a warm-up query first (Issue #311).

See docs/write-support-limitations.md for the full limitations reference.

Resources

• Acceptance Testing Notebook - Interactive examples and validation
• Type Stubs - Complete API type hints for IDE support
• Main Project README - CQLite project overview and documentation
• Write Support Guide - Detailed write documentation
• Issue Tracker - Report bugs or request features

License

MIT OR Apache-2.0

Links

• GitHub Repository
• PyPI Package
• Documentation