Velodb Best Practices

VeloDB Best Practices

Problem-first table design intelligence for Apache Doris. 37 rules, 7 use case templates, 4 sizing guides. All details in references/ directory and compiled AGENTS.md.

1 ▸ Problem-First Routing

I need to build…

My query is slow after evidence shows…

For live slow-query or runtime diagnosis, do not use this table as the first response. First read references/cli-investigation.md and collect or attempt evidence (profile get, profile list, profile history, tablet, EXPLAIN, or auth status). Use this table only after evidence points to the symptom.

2 ▸ Pre-Flight Checklist (Before Any CREATE TABLE)

Run through this checklist in order. Each step references the relevant rule:

• Data model — UNIQUE (updates?) vs DUPLICATE (append?) vs AGGREGATE (pre-agg only?) → schema-model-choose-for-workload
• Partition strategy — Time-series? AUTO PARTITION preferred. Small table? Skip. Do NOT combine AUTO with dynamic_partition. → schema-partition-*
• Bucket key + count — HASH on JOIN key. Calculate explicit count: daily_GB / target_tablet_GB. Use explicit fallback counts when volume is unknown: 3 for small dimensions, 8 for medium tables, 16-32 for large daily fact tables. → schema-bucket-*
• Sort key order — High-selectivity first, fixed-length before VARCHAR → schema-keys-*
• Data types — Native types, not STRING. DECIMAL not FLOAT. → schema-types-*
• Indexes — BloomFilter for equality, Inverted for text, NGram for LIKE → schema-index-*
• Properties — MoW enabled? Compression? Cloud mode replication_num=1? → schema-props-*
• DDL hard constraints (VeloDB rejects DDL if any violated):
  • UNIQUE KEY + PARTITION BY RANGE → partition column MUST be in the UNIQUE KEY: UNIQUE KEY(id, dt) PARTITION BY RANGE(dt)
  • Key columns must be the FIRST N columns in schema, same order — put key cols first, non-key after. Example: UNIQUE KEY(account_id, symbol) means schema must start with account_id, symbol, ... — never place non-key columns between key columns
  • store_row_column = "true" only works on UNIQUE MoW — NOT on AGGREGATE or DUPLICATE
  • AUTO PARTITION requires date_trunc() AND empty parens: AUTO PARTITION BY RANGE(date_trunc(col, 'day')) () — bare column name fails, missing () fails
  • Dynamic partition requires explicit PARTITION BY RANGE(col) () clause in DDL — properties alone are not enough
  • Do not set dynamic_partition.buckets; put the numeric count only in DISTRIBUTED BY HASH(col) BUCKETS N
  • compaction_policy = "time_series" only for DUPLICATE tables — fails on UNIQUE
  • Async MV refresh: use REFRESH AUTO ON SCHEDULE EVERY 10 MINUTE or REFRESH COMPLETE ON SCHEDULE EVERY 10 MINUTE — NOT REFRESH SCHEDULE EVERY, NOT REFRESH ASYNC EVERY(INTERVAL ...). Minimum interval: 1 MINUTE
  • MV using NOW()/CURDATE(): add PROPERTIES ("enable_nondeterministic_function" = "true")
  • BOOLEAN defaults must be quoted: DEFAULT "true" not DEFAULT TRUE
  • BloomFilter index: use PROPERTIES ("bloom_filter_columns" = "col1,col2") — NOT inline INDEX ... USING BLOOM FILTER
  • AGGREGATE column syntax: aggregation function BEFORE default: col BIGINT SUM DEFAULT "0" — NOT col BIGINT DEFAULT "0" SUM
  • AGGREGATE DEFAULT "null" only works for VARCHAR — fails on INT, DATE, DECIMAL, BIGINT. Omit DEFAULT entirely for REPLACE_IF_NOT_NULL on non-string types: vip_level INT REPLACE_IF_NOT_NULL (not DEFAULT "null")
  • enable_unique_key_partial_update is a session variable, NOT a table property
  • Full details: schema-ddl-gotchas

2b ▸ DDL Templates (copy the closest match, customize columns)

For each CREATE TABLE, select the closest template below. Customize column names, types, bucket count, and partition settings. Do NOT write DDL from scratch.

T1: Append-only events/logs (DUPLICATE)

CREATE TABLE events (
    entity_id    VARCHAR(64)  NOT NULL,
    event_time   DATETIME     NOT NULL,
    event_type   VARCHAR(50)  NOT NULL,
    payload      VARIANT
) DUPLICATE KEY(entity_id, event_time, event_type)
PARTITION BY RANGE(event_time) ()
DISTRIBUTED BY HASH(entity_id) BUCKETS 10
PROPERTIES (
    "dynamic_partition.enable" = "true",
    "dynamic_partition.time_unit" = "DAY",
    "dynamic_partition.start" = "-90",
    "dynamic_partition.end" = "3",
    "dynamic_partition.prefix" = "p",
    "compression" = "zstd",
    "compaction_policy" = "time_series",
    "replication_num" = "1"
);

T2: Updatable with partition (UNIQUE MoW + CDC)

CREATE TABLE orders (
    order_id     BIGINT       NOT NULL,
    order_time   DATETIME     NOT NULL,
    update_time  DATETIME     NOT NULL,
    status       VARCHAR(20),
    amount       DECIMAL(18,2)
) UNIQUE KEY(order_id, order_time)
PARTITION BY RANGE(order_time) ()
DISTRIBUTED BY HASH(order_id) BUCKETS 5
PROPERTIES (
    "enable_unique_key_merge_on_write" = "true",
    "function_column.sequence_col" = "update_time",
    "dynamic_partition.enable" = "true",
    "dynamic_partition.time_unit" = "DAY",
    "dynamic_partition.start" = "-365",
    "dynamic_partition.end" = "3",
    "dynamic_partition.prefix" = "p",
    "replication_num" = "1"
);

T3: Small dimension / lookup (UNIQUE, no partition)

CREATE TABLE dim_product (
    product_id   INT          NOT NULL,
    name         VARCHAR(200),
    category     VARCHAR(50)
) UNIQUE KEY(product_id)
DISTRIBUTED BY HASH(product_id) BUCKETS 3
PROPERTIES (
    "enable_unique_key_merge_on_write" = "true",
    "replication_num" = "1"
);

T4: Pre-aggregated KPIs (AGGREGATE)

CREATE TABLE daily_kpi (
    stat_date    DATE         NOT NULL,
    dimension    VARCHAR(50)  NOT NULL,
    metric_sum   BIGINT       SUM DEFAULT "0",
    metric_max   DOUBLE       MAX DEFAULT "0",
    unique_users BITMAP       BITMAP_UNION
) AGGREGATE KEY(stat_date, dimension)
PARTITION BY RANGE(stat_date) ()
DISTRIBUTED BY HASH(dimension) BUCKETS 3
PROPERTIES (
    "dynamic_partition.enable" = "true",
    "dynamic_partition.time_unit" = "MONTH",
    "dynamic_partition.start" = "-12",
    "dynamic_partition.end" = "1",
    "dynamic_partition.prefix" = "p",
    "replication_num" = "1"
);

T5: Point query / API serving (UNIQUE MoW + row store)

CREATE TABLE user_profiles (
    user_id      BIGINT       NOT NULL,
    update_time  DATETIME     NOT NULL,
    name         VARCHAR(100),
    data         VARIANT
) UNIQUE KEY(user_id)
DISTRIBUTED BY HASH(user_id) BUCKETS 5
PROPERTIES (
    "enable_unique_key_merge_on_write" = "true",
    "function_column.sequence_col" = "update_time",
    "store_row_column" = "true",
    "light_schema_change" = "true",
    "replication_num" = "1"
);

3 ▸ Connection & VeloCLI

Detect VeloCLI

Before running any queries, detect the CLI binary:

1. Check VELOCLI_PATH env var — if set, use that binary path
2. command -v velocli — use from PATH
3. command -v sdbcli — only for explicit SelectDB environments
4. If none available: fall back to mysql client (see references/start-*.md)

When VeloCLI is available, prefer it for all operations:

Runtime Query Investigation

For slow queries or runtime performance issues, read references/cli-investigation.md.

• Evidence first is mandatory: collect or attempt profile, tablet, DDL, stats, EXPLAIN, history, active-query, or connection evidence before forming hypotheses. If evidence cannot be collected locally, state that and provide the exact commands to run
• Prefer existing profiles: use profile get <query_id>, profile list, or profile history before re-executing SQL
• Proactive discovery: for vague slow-query reports, start with auth status, profile list --active, and recent profile list before asking the user for more context
• Safety gate: before running user SQL with --profile, check whether it is safe (no DDL, no mutation, no unbounded scan). For unknown, peak-hour, or expensive SQL, run velocli sql "EXPLAIN <query>" --format json first and ask confirmation or request an existing query_id
• Hypotheses, not verdicts: diagnostic mappings are heuristics. Present evidence, likely cause, what to check next, and when the conclusion may be wrong
• If velocli is unavailable, fall back to SQL commands listed in the reference
• Always use --format json for structured agent-readable output

Quick-start guides

• references/start-cloud.md — VeloDB Cloud
• references/start-self-hosted.md — Self-hosted / BYOC / on-prem

4 ▸ Cluster Sizing

Sizing guides are in:

• references/sizing-fe.md — FE node sizing
• references/sizing-be-integrated.md — BE sizing (integrated storage)
• references/sizing-be-cloud.md — BE sizing (cloud / storage-compute)
• references/sizing-storage-formula.md — Storage calculation formula

5 ▸ Rule Index by Category

Data Model — CRITICAL (4 rules)

• schema-model-choose-for-workload — DUP vs UNIQUE vs AGG decision tree
• schema-model-prefer-mow — Always MoW for UNIQUE tables
• schema-model-avoid-agg-for-updates — AGG cannot UPDATE/DELETE
• schema-model-sequence-col-for-cdc — Sequence column for out-of-order CDC

Partition Strategy — CRITICAL (4 rules)

• schema-partition-range-for-timeseries — RANGE for time-series
• schema-partition-dynamic-ttl — Dynamic partition for automated TTL
• schema-partition-auto-on-demand — AUTO for sporadic data
• schema-partition-skip-for-small — Skip partitioning under 1 GB

Bucket Strategy — CRITICAL (5 rules)

• schema-bucket-hash-vs-random — HASH for pruning, RANDOM for DUP only
• schema-bucket-high-cardinality-key — Choose high-cardinality column
• schema-bucket-composite-for-skew — Composite key to fix data skew
• schema-bucket-target-size — Target 1-10 GB per tablet
• schema-bucket-cloud-mandatory-hash — Cloud MoW requires HASH

Sort Key — CRITICAL (5 rules)

• schema-keys-selectivity-first — High selectivity first
• schema-keys-fixed-length-types — Fixed-length before VARCHAR
• schema-keys-prefix-index-limits — 36 bytes max, VARCHAR terminates it
• schema-keys-cluster-key-for-mow — Cluster key for UNIQUE tables
• schema-keys-avoid-float — No FLOAT/DOUBLE in sort key

Data Types — HIGH (5 rules)

• schema-types-native-vs-string — Native types, not STRING
• schema-types-zonemap-limitations — JSON/ARRAY disable ZoneMap
• schema-types-variant-json — VARIANT for semi-structured JSON
• schema-types-bitmap-count-distinct — BITMAP_UNION for exact count-distinct
• schema-types-doris-specifics — DATETIME precision, VARCHAR vs STRING

Indexes — HIGH (7 rules)

• schema-index-bloomfilter — BloomFilter for equality
• schema-index-inverted — Inverted for text/range
• schema-index-ngram-for-like — NGram for LIKE %pattern%
• schema-index-bitmap — Bitmap for medium cardinality
• schema-index-vector — HNSW/IVF for ANN search
• schema-index-text-search — Full-text MATCH + BM25

Query Acceleration — HIGH (3 rules)

• schema-mv-sync-rollup — Sync MV for single-table aggregation
• schema-mv-async-join — Async MV for multi-table JOIN
• schema-mv-async-limits — Operational limits (50M rows, 3 concurrent)

Table Properties — HIGH/MEDIUM (2 rules)

• schema-props-cloud-forced — Cloud mode forced properties
• schema-props-compression — LZ4 vs ZSTD compression

Caching — MEDIUM (2 rules)

• schema-cache-file-cache — File cache for cloud mode
• schema-cache-query-partition — Query and partition cache