# Identifying Slow Queries Slow commands can impact Valkey performance, especially under high concurrency or when inefficient data access patterns are used. Whether you’re running Valkey on Elestio via the dashboard, inside a Docker Compose setup, or accessing it through the CLI, Valkey includes powerful introspection tools like the slow log and latency tracking. This guide shows how to detect slow operations using Valkey’s built-in slowlog, analyze latency issues, and optimize performance through configuration tuning and query best practices. ## **Inspecting Slow Commands from the Terminal** Valkey supports the Redis-compatible SLOWLOG feature to record commands that exceed a configured execution time threshold. These logs are useful to spot expensive operations and server stalls. ##### **Connect to Your Valkey Instance via Terminal** Use valkey-cli or redis-cli to connect to your Valkey instance: ``` valkey-cli -h -p -a ``` Replace <host>, <port>, and <password> with the credentials available in your Elestio dashboard. ##### **View the Slowlog Threshold** Check what execution time (in microseconds) is considered “slow”: ``` CONFIG GET slowlog-log-slower-than ``` The default is 10000 (10 milliseconds). Commands slower than this will be logged. ##### **View the Slow Query Logs** To retrieve recent slow operations: ```bash SLOWLOG GET 10 ``` This shows the 10 most recent slowlog entries, each with: - The command that was executed - The timestamp - Execution duration in microseconds - Any arguments passed to the command ## **Analyzing Inside Docker Compose** If you’re running Valkey via Docker Compose, you can inspect slow queries from within the container environment. ##### **Access the Valkey Container** Launch a shell in your container: ``` docker-compose exec valkey bash ``` Connect to Valkey using: ``` valkey-cli -a $VALKEY_PASSWORD ``` Ensure that VALKEY\_PASSWORD is defined in your .env file or Compose environment variables. ##### **Adjust Slowlog Settings** You can view or modify the slowlog threshold dynamically: ``` CONFIG SET slowlog-log-slower-than 5000 ``` This temporarily changes the threshold to 5 milliseconds, which is useful for debugging under lower latency conditions. ##### **Increase the Number of Stored Entries** Check how many slowlog entries are retained: ```bash CONFIG GET slowlog-max-len ``` To store more slowlog entries: ```bash CONFIG SET slowlog-max-len 256 ``` This helps in long-running investigations or during load testing. ## **Using the Latency Monitoring Feature** Valkey inherits Redis’s latency monitoring tools, providing additional insights beyond command duration such as fork stalls, I/O blocks, or memory pressure. ##### **Enable Latency Monitoring** Latency tracking is often enabled by default. Run: ``` LATENCY DOCTOR ``` This provides a high-level diagnostic report of system latency spikes and potential root causes, including slow commands, AOF rewrites, and blocking operations. ##### **View Latency History for Specific Events** Track the latency of specific operations like: ```bash LATENCY HISTORY command ``` Other event categories include: - fork – Background save or AOF rewrite delays - aof-write – Append-only file sync lag - command – General command execution delays ## **Understanding and Resolving Common Bottlenecks** Valkey performance can degrade due to specific patterns of usage, large keys, blocking commands, or non-optimized pipelines. ##### **Common Causes of Slowness** - Large keys: Commands like LRANGE, SMEMBERS, or HGETALL on large datasets. - Blocking commands: Such as BLPOP, BRPOP, or long-running Lua scripts. - Forking delays: Caused by SAVE or AOF background rewriting. ##### **Best Practices for Performance** - Use SCAN instead of KEYS to iterate large keyspaces safely. - Limit range queries: Use LRANGE 0 99 instead of fetching full lists. - Enable pipelining: Reduce round trips by batching commands. - Avoid multi-key ops: Especially in clustered deployments, where they can cause performance issues or fail. ## **Optimizing with Configuration Changes** Valkey performance can be significantly tuned by adjusting memory and persistence-related settings. ##### **Common Tuning Examples** ```bash CONFIG SET maxmemory-policy allkeys-lru CONFIG SET save "" ``` These adjust eviction and persistence behaviours. Use these with caution: - Disabling RDB/AOF improves speed but removes durability. - LRU/TTL policies control memory usage under load.