find-hypertable-candidates（寻找超稳定候选者）

PostgreSQL Hypertable Candidate Analysis

Identify tables that would benefit from TimescaleDB hypertable conversion. After identification, use the companion "migrate-postgres-tables-to-hypertables" skill for configuration and migration.

TimescaleDB Benefits

Performance gains: 90%+ compression, fast time-based queries, improved insert performance, efficient aggregations, continuous aggregates for materialization (dashboards, reports, analytics), automatic data management (retention, compression).

Best for insert-heavy patterns:

• Time-series data (sensors, metrics, monitoring)
• Event logs (user events, audit trails, application logs)
• Transaction records (orders, payments, financial)
• Sequential data (auto-incrementing IDs with timestamps)
• Append-only datasets (immutable records, historical)

Requirements: Large volumes (1M+ rows), time-based queries, infrequent updates

Step 1: Database Schema Analysis

Option A: From Database Connection

Table statistics and size

-- Get all tables with row counts and insert/update patterns
WITH table_stats AS (
    SELECT
        schemaname, tablename,
        n_tup_ins as total_inserts,
        n_tup_upd as total_updates,
        n_tup_del as total_deletes,
        n_live_tup as live_rows,
        n_dead_tup as dead_rows
    FROM pg_stat_user_tables
),
table_sizes AS (
    SELECT
        schemaname, tablename,
        pg_size_pretty(pg_total_relation_size(schemaname||'.'||tablename)) as total_size,
        pg_total_relation_size(schemaname||'.'||tablename) as total_size_bytes
    FROM pg_tables
    WHERE schemaname NOT IN ('information_schema', 'pg_catalog')
)
SELECT
    ts.schemaname, ts.tablename, ts.live_rows,
    tsize.total_size, tsize.total_size_bytes,
    ts.total_inserts, ts.total_updates, ts.total_deletes,
    ROUND(CASE WHEN ts.live_rows > 0
          THEN (ts.total_inserts::float / ts.live_rows) * 100
          ELSE 0 END, 2) as insert_ratio_pct
FROM table_stats ts
JOIN table_sizes tsize ON ts.schemaname = tsize.schemaname AND ts.tablename = tsize.tablename
ORDER BY tsize.total_size_bytes DESC;

Look for:

• mostly insert-heavy patterns (less updates/deletes)
• big tables (1M+ rows or 100MB+)

Index patterns

-- Identify common query dimensions
SELECT schemaname, tablename, indexname, indexdef
FROM pg_indexes
WHERE schemaname NOT IN ('information_schema', 'pg_catalog')
ORDER BY tablename, indexname;

Look for:

• Multiple indexes with timestamp/created_at columns → time-based queries
• Composite (entity_id, timestamp) indexes → good candidates
• Time-only indexes → time range filtering common

Query patterns (if pg_stat_statements available)

-- Check availability
SELECT EXISTS (SELECT 1 FROM pg_extension WHERE extname = 'pg_stat_statements');

-- Analyze expensive queries for candidate tables
SELECT query, calls, mean_exec_time, total_exec_time
FROM pg_stat_statements
WHERE query ILIKE '%your_table_name%'
ORDER BY total_exec_time DESC LIMIT 20;

✅ Good patterns: Time-based WHERE, entity filtering combined with time-based qualifiers, GROUP BY time_bucket, range queries over time ❌ Poor patterns: Non-time lookups with no time-based qualifiers in same query (WHERE email = ...)

Constraints

-- Check migration compatibility
SELECT conname, contype, pg_get_constraintdef(oid) as definition
FROM pg_constraint
WHERE conrelid = 'your_table_name'::regclass;

Compatibility:

• Primary keys (p): Must include partition column or ask user if can be modified
• Foreign keys (f): Plain→Hypertable and Hypertable→Plain OK, Hypertable→Hypertable NOT supported
• Unique constraints (u): Must include partition column or ask user if can be modified
• Check constraints (c): Usually OK

Option B: From Code Analysis

✅ GOOD Patterns

# Append-only logging
INSERT INTO events (user_id, event_time, data) VALUES (...);
# Time-series collection
INSERT INTO metrics (device_id, timestamp, value) VALUES (...);
# Time-based queries
SELECT * FROM metrics WHERE timestamp >= NOW() - INTERVAL '24 hours';
# Time aggregations
SELECT DATE_TRUNC('day', timestamp), COUNT(*) GROUP BY 1;

❌ POOR Patterns

# Frequent updates to historical records
UPDATE users SET email = ..., updated_at = NOW() WHERE id = ...;
# Non-time lookups
SELECT * FROM users WHERE email = ...;
# Small reference tables
SELECT * FROM countries ORDER BY name;

Schema Indicators

✅ GOOD:

• Has timestamp/timestamptz column
• Multiple indexes with timestamp-based columns
• Composite (entity_id, timestamp) indexes

❌ POOR:

• Mostly indexes with non-time-based columns (on columns like email, name, status, etc.)
• Columns that you expect to be updated over time (updated_at, updated_by, status, etc.)
• Unique constraints on non-time fields
• Frequent updated_at modifications
• Small static tables

Special Case: ID-Based Tables

Sequential ID tables can be candidates if:

• Insert-mostly pattern / updates are either infrequent or only on recent records.
• If updates do happen, they occur on recent records (such as an order status being updated orderered->processing->delivered. Note once an order is delivered, it is unlikely to be updated again.)
• IDs correlate with time (as is the case for serial/auto-incrementing IDs/GENERATED ALWAYS AS IDENTITY)
• ID is the primary query dimension
• Recent data accessed more often (frequently the case in ecommerce, finance, etc.)
• Time-based reporting common (e.g. monthly, daily summaries/analytics)

CREATE TABLE orders (
    id BIGSERIAL PRIMARY KEY,           -- Can partition by ID
    user_id BIGINT,
    created_at TIMESTAMPTZ DEFAULT NOW() -- For sparse indexes
);

Note: For ID-based tables where there is also a time column (created_at, ordered_at, etc.), you can partition by ID and use sparse indexes on the time column. See the migrate-postgres-tables-to-hypertables skill for details.

Step 2: Candidacy Scoring (8+ points = good candidate)

Time-Series Characteristics (5+ points needed)

• Has timestamp/timestamptz column: 3 points
• Data inserted chronologically: 2 points
• Queries filter by time: 2 points
• Time aggregations common: 2 points

Scale & Performance (3+ points recommended)

• Large table (1M+ rows or 100MB+): 2 points
• High insert volume: 1 point
• Infrequent updates to historical: 1 point
• Range queries common: 1 point
• Aggregation queries: 2 points

Data Patterns (bonus)

• Contains entity ID for segmentation (device_id, user_id, product_id, symbol, etc.): 1 point
• Numeric measurements: 1 point
• Log/event structure: 1 point

Common Patterns

✅ GOOD Candidates

✅ Event/Log Tables (user_events, audit_logs)

CREATE TABLE user_events (
    id BIGSERIAL PRIMARY KEY,
    user_id BIGINT,
    event_type TEXT,
    event_time TIMESTAMPTZ DEFAULT NOW(),
    metadata JSONB
);
-- Partition by id, segment by user_id, enable minmax sparse_index on event_time

✅ Sensor/IoT Data (sensor_readings, telemetry)

CREATE TABLE sensor_readings (
    device_id TEXT,
    timestamp TIMESTAMPTZ,
    temperature DOUBLE PRECISION,
    humidity DOUBLE PRECISION
);
-- Partition by timestamp, segment by device_id, minmax sparse indexes on temperature and humidity

✅ Financial/Trading (stock_prices, transactions)

CREATE TABLE stock_prices (
    symbol VARCHAR(10),
    price_time TIMESTAMPTZ,
    open_price DECIMAL,
    close_price DECIMAL,
    volume BIGINT
);
-- Partition by price_time, segment by symbol, minmax sparse indexes on open_price and close_price and volume

✅ System Metrics (monitoring_data)

CREATE TABLE system_metrics (
    hostname TEXT,
    metric_time TIMESTAMPTZ,
    cpu_usage DOUBLE PRECISION,
    memory_usage BIGINT
);
-- Partition by metric_time, segment by hostname, minmax sparse indexes on cpu_usage and memory_usage

❌ POOR Candidates

❌ Reference Tables (countries, categories)

CREATE TABLE countries (
    id SERIAL PRIMARY KEY,
    name VARCHAR(100),
    code CHAR(2)
);
-- Static data, no time component

❌ User Profiles (users, accounts)

CREATE TABLE users (
    id BIGSERIAL PRIMARY KEY,
    email VARCHAR(255),
    created_at TIMESTAMPTZ,
    updated_at TIMESTAMPTZ
);
-- Accessed by ID, frequently updated, has timestamp but it's not the primary query dimension (the primary query dimension is id or email)

❌ Settings/Config (user_settings)

CREATE TABLE user_settings (
    user_id BIGINT PRIMARY KEY,
    theme VARCHAR(20),       -- Changes: light -> dark -> auto
    language VARCHAR(10),    -- Changes: en -> es -> fr
    notifications JSONB,     -- Frequent preference updates
    updated_at TIMESTAMPTZ
);
-- Accessed by user_id, frequently updated, has timestamp but it's not the primary query dimension (the primary query dimension is user_id)

Analysis Output Requirements

For each candidate table provide:

• Score: Based on criteria (8+ = strong candidate)
• Pattern: Insert vs update ratio
• Access: Time-based vs entity lookups
• Size: Current size and growth rate
• Queries: Time-range, aggregations, point lookups

Focus on insert-heavy patterns with time-based or sequential access. Tables scoring 8+ points are strong candidates for conversion.