Scalar Types, Timestamps / Dates, UUID / timeuuid, Decimal / Varint, Blob, Duration, and Conversion

Learning outcomes

AtlasMart is ingesting order totals, event clocks, identifiers, checksums, service windows, and high-precision counters from multiple services. Choosing text for everything would move validation bugs into application code and make ordering, arithmetic, range checks, and driver decoding ambiguous. Cassandra Query Language (CQL) scalar types are part of the storage contract: they define accepted values, binary representation, comparison behavior, and the native-protocol type a driver decodes.

1. A type is a storage and comparison contract

Cassandra types are not cosmetic aliases. int and bigint are fixed-width signed integers with different ranges; varint is arbitrary precision. decimal stores arbitrary-precision decimal values and is a better semantic fit for exact monetary quantities than binary floating point. uuid is an opaque universally unique identifier. timeuuid is specifically a version-1 UUID whose timestamp component can support time ordering and conversion functions. blob stores uninterpreted bytes, expressed in CQL with a 0x-prefixed hexadecimal literal. duration stores months, days, and nanoseconds as separate components; because calendar months do not have one fixed number of seconds, do not reduce duration to a single millisecond count without a reference date.

2. Lab: store and inspect representative scalar values

# Verify the shared course lab if it already exists.docker exec atlasmart-cass-1 nodetool versiondocker exec atlasmart-cass-1 nodetool status# Standalone local recreation path. Skip resources that already exist.docker network inspect atlasmart-cassandra >/dev/null 2>&1 || docker network create atlasmart-cassandradocker volume create atlasmart-cass-1-datadocker volume create atlasmart-cass-2-datadocker volume create atlasmart-cass-3-datadocker inspect atlasmart-cass-1 >/dev/null 2>&1 || docker run -d --name atlasmart-cass-1 --hostname atlasmart-cass-1 --network atlasmart-cassandra -e CASSANDRA_CLUSTER_NAME=atlasmart-course -e CASSANDRA_DC=dc1 -e CASSANDRA_RACK=rack1 -e CASSANDRA_ENDPOINT_SNITCH=GossipingPropertyFileSnitch -e CASSANDRA_NUM_TOKENS=16 -v atlasmart-cass-1-data:/var/lib/cassandra cassandra:5.0.9# Wait for node 1 to answer before starting peers.docker exec atlasmart-cass-1 nodetool statusdocker inspect atlasmart-cass-2 >/dev/null 2>&1 || docker run -d --name atlasmart-cass-2 --hostname atlasmart-cass-2 --network atlasmart-cassandra -e CASSANDRA_CLUSTER_NAME=atlasmart-course -e CASSANDRA_DC=dc1 -e CASSANDRA_RACK=rack2 -e CASSANDRA_ENDPOINT_SNITCH=GossipingPropertyFileSnitch -e CASSANDRA_NUM_TOKENS=16 -e CASSANDRA_SEEDS=atlasmart-cass-1 -v atlasmart-cass-2-data:/var/lib/cassandra cassandra:5.0.9docker inspect atlasmart-cass-3 >/dev/null 2>&1 || docker run -d --name atlasmart-cass-3 --hostname atlasmart-cass-3 --network atlasmart-cassandra -e CASSANDRA_CLUSTER_NAME=atlasmart-course -e CASSANDRA_DC=dc1 -e CASSANDRA_RACK=rack3 -e CASSANDRA_ENDPOINT_SNITCH=GossipingPropertyFileSnitch -e CASSANDRA_NUM_TOKENS=16 -e CASSANDRA_SEEDS=atlasmart-cass-1 -v atlasmart-cass-3-data:/var/lib/cassandra cassandra:5.0.9# Continue only after all nodes show UN.docker exec atlasmart-cass-1 nodetool statusdocker exec atlasmart-cass-1 cqlsh -e "CREATE KEYSPACE IF NOT EXISTS atlasmart_types WITH replication = {'class':'NetworkTopologyStrategy','dc1':3};"docker exec atlasmart-cass-1 cqlsh -e "DESCRIBE KEYSPACE atlasmart_types"

CREATE TABLE atlasmart_types.scalar_probe (    tenant_id uuid,    event_id timeuuid,    recorded_at timestamp,    business_date date,    opening_time time,    order_total decimal,    huge_sequence varint,    checksum blob,    fulfilment_sla duration,    note text,    PRIMARY KEY ((tenant_id), event_id)) WITH CLUSTERING ORDER BY (event_id DESC)  AND compaction = {'class':'UnifiedCompactionStrategy'};DESCRIBE TABLE atlasmart_types.scalar_probe;

CONSISTENCY LOCAL_QUORUM;INSERT INTO atlasmart_types.scalar_probe(tenant_id,event_id,recorded_at,business_date,opening_time,order_total,huge_sequence,checksum,fulfilment_sla,note)VALUES(11111111-1111-1111-1111-111111111111, now(), '2026-09-07T12:00:00Z', '2026-09-07', '12:34:56.123456789', 1299.95, 123456789012345678901234567890, 0x41424344, 2d3h, 'paid');SELECT tenant_id,event_id,to_timestamp(event_id),to_unix_timestamp(event_id),recorded_at,business_date,opening_time,order_total,huge_sequence,checksum,fulfilment_slaFROM atlasmart_types.scalar_probeWHERE tenant_id=11111111-1111-1111-1111-111111111111;

The exact generated event_id differs every run. What matters is that to_timestamp(event_id) and to_unix_timestamp(event_id) decode the embedded version-1 UUID time, while the separately stored recorded_at remains an ordinary timestamp. Cassandra 5.0 uses the snake_case conversion names; older camelCase spellings are deprecated.

3. Driver decoding is part of the contract

An application driver does not receive a bag of strings. Native-protocol metadata identifies each CQL type, and the codec layer maps it to language types. The optional Java example below uses Apache Cassandra Java Driver 4.19.3; exact imports/configuration should be rechecked if you use another driver or release.

Row row = session.execute(    "SELECT event_id, recorded_at, order_total, huge_sequence, checksum, fulfilment_sla " +    "FROM atlasmart_types.scalar_probe WHERE tenant_id=?",    UUID.fromString("11111111-1111-1111-1111-111111111111")).one();UUID eventId = row.getUuid("event_id");Instant recordedAt = row.getInstant("recorded_at");BigDecimal total = row.getBigDecimal("order_total");BigInteger sequence = row.getBigInteger("huge_sequence");ByteBuffer checksum = row.getByteBuffer("checksum");CqlDuration sla = row.getCqlDuration("fulfilment_sla");

4. Production judgment

Scalar choice affects partition-key serialization, clustering comparison, payload size, CPU for numeric conversion, application serialization, and migration compatibility. Do not change a column's type casually: modern CQL removed arbitrary ALTER TYPE changes for table columns, so incompatible type redesign normally means a new column/table and controlled migration. For identifiers, use uuid unless time ordering is part of the contract; for event ordering, timeuuid can help but does not replace a separately modeled business timestamp. For money, avoid binary floating point when exact decimal semantics are required. For blob, validate size/content at the application boundary because Cassandra cannot interpret your encoding. Duration arithmetic and cross-language decoding deserve explicit tests.

Verification checklist

• The scalar table schema matches the intended value domains rather than generic text columns.
• timeuuid conversion produces a timestamp/epoch value derived from the generated identifier.
• Decimal/varint values round-trip without fixed-width truncation.
• Blob output is still opaque bytes; interpretation remains outside Cassandra.
• Optional driver decoding uses typed getters rather than string parsing.

# Destructive only to this disposable chapter keyspace.docker exec atlasmart-cass-1 cqlsh -e "DROP KEYSPACE IF EXISTS atlasmart_types;"# Keep shared course containers for Chapter 09, or remove them for a full reset:# docker rm -f atlasmart-cass-1 atlasmart-cass-2 atlasmart-cass-3# docker volume rm atlasmart-cass-1-data atlasmart-cass-2-data atlasmart-cass-3-data# docker network rm atlasmart-cassandra

Summary and next bridge

Scalar types are executable domain constraints, not decoration. Next we move from one typed value per cell to lists, sets, and maps—where growth, element mutation, TTL, and tombstone behavior become part of the storage cost.

Authoritative references

• CQL data types — scalar, collection, tuple, user-defined type, frozen, and literal semantics.
• Creating collections — bounded collection guidance and current collection guardrails.
• CQL data definition — static-column behavior, table/type definitions, and schema restrictions.
• CREATE TABLE reference — frozen/non-frozen UDT and static-column examples.
• Tombstones — deletion markers, grace, reads, and compaction implications.
• Apache Cassandra downloads — current server and Java-driver release baselines.