docs: add pg logs blog (#981)

* add postgres logs

* update

* Update content/blog/postgres-logs.md

Co-authored-by: Copilot <[email protected]>

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Co-authored-by: Copilot <[email protected]>

Author: adela-bytebase

content/blog/postgres-logs.md

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+---
+title: 'Postgres Logs Explained: A Practical Guide for Production'
+author: Adela
+updated_at: 2026/01/07 18:00:00
+feature_image: /content/blog/postgres-logs/cover.webp
+tags: Explanation
+description: A guide to Postgres logs in production.
+---
+
+Logs are one of the most important, and most misunderstood parts of running **Postgres** in production. When configured well, Postgres logs help you debug incidents, understand performance issues, and gain visibility into database behavior. When configured poorly, they create noise, increase load, and still fail to answer the questions you care about.
+
+This guide explains **what Postgres logs are, how logging works, which settings matter most, and how to use logs effectively in real systems**, without overcomplicating things.
+
+---
+
+## What Postgres logs are
+
+**Postgres logs record what the database server is doing.** They capture server-side events such as:
+
+- SQL statements (optionally)
+- Slow queries
+- Errors and warnings
+- Connection and disconnection events
+- Lock waits and deadlocks
+- Background activity like checkpoints and autovacuum
+
+They are primarily an **operational tool**. Engineers rely on Postgres logs to answer questions like:
+
+- Why is this query slow?
+- Why are connections spiking?
+- What caused this error?
+- Is the database under unusual load?
+
+Postgres logs are generated by the database server itself and are independent of application logs.
+
+## How Postgres logging works (high level)
+
+By default, Postgres writes log output to `stderr`. When the `logging_collector` is enabled, Postgres captures this output and writes it to log files on disk.
+
+Key points to know:
+
+- Logs are written on the database server, not the client
+- Log files can be plain text or structured (`csvlog`)
+- Log rotation can be based on time or file size
+- Retention is your responsibility — Postgres does not manage it automatically
+
+#### Common log formats
+
+- **Plain text logs**
+  Easy to read, harder to parse at scale.
+
+- **CSV logs (`csvlog`)**
+  Structured, machine-friendly, and much easier to ingest into log systems.
+
+If you plan to analyze logs beyond manual inspection, `csvlog` is usually the better choice.
+
+## The most important Postgres logging parameters
+
+Postgres exposes many logging options, but only a subset matter for most production systems. It’s best to think about them by **intent**, not alphabetically.
+
+### 🔍 Query performance and slow queries
+
+This is where most teams start — and where most mistakes happen.
+
+#### `log_min_duration_statement`
+
+Logs statements that run longer than a specified duration (in milliseconds).
+
+```conf
+log_min_duration_statement = 500
+```
+
+This logs queries that take longer than 500 ms and is often the **best default** for production systems.
+
+#### `log_duration`
+
+Logs how long every statement took.
+
+Useful for debugging, but very noisy if left on permanently.
+
+#### `log_statement`
+
+Controls which statements are logged.
+
+Values include `none`, `ddl`, `mod` and `all`.
+
+```conf
+log_statement = none
+```
+
+Setting `log_statement = all` in production is rarely a good idea — it generates huge volumes of logs and can noticeably impact performance.
+
+### 🔌 Connections and authentication
+
+Connection-related logs help diagnose spikes, leaks, and unexpected traffic.
+
+Key settings are `log_connections`, `log_disconnections` and `log_hostname`.
+
+These are especially useful when:
+
+- Using connection pools
+- Investigating sudden increases in load
+- Debugging authentication issues
+
+They are typically safe to enable, but still generate noticeable volume on busy systems.
+
+### ⚠️ Errors, locks, and failures
+
+These settings help explain *why* queries are blocked or failing.
+
+- `log_error_verbosity`
+  Controls how much detail is logged for errors.
+
+- `log_lock_waits`
+  Logs statements that wait longer than `deadlock_timeout` for locks.
+
+- `deadlock_timeout`
+  How long Postgres waits before checking for deadlocks.
+
+Together, these settings are invaluable for diagnosing:
+
+- Lock contention
+- Deadlocks
+- Long-running transactions blocking others
+
+### 🧠 Context: making Postgres logs readable
+
+Logs without context are frustrating. This is where `log_line_prefix` matters.
+
+```conf
+log_line_prefix = '%m [%p] %u@%d '
+```
+
+This adds:
+
+- timestamp
+- process ID
+- user
+- database name
+
+Without a proper prefix, it becomes very difficult to correlate log lines with:
+
+- applications
+- users
+- specific databases
+
+A good `log_line_prefix` dramatically improves log usability with minimal overhead.
+
+## Common Postgres logging mistakes
+
+Even experienced teams run into these.
+
+### Logging everything
+
+Turning on full statement logging in production creates massive noise and real performance cost — often without delivering useful insight.
+
+### Enabling too many options at once
+
+Logging connections, disconnections, durations, statements, and background activity simultaneously can overwhelm both storage and humans.
+
+### Missing context
+
+Logs without user, database, or timestamp information are hard to interpret and nearly impossible to analyze at scale.
+
+### No retention strategy
+
+Keeping logs forever increases cost and risk. Keeping them too briefly makes post-incident analysis impossible.
+
+### Collecting logs but never using them
+
+Logs should answer questions. If nobody looks at them, they’re just expensive text files.
+
+## Performance impact of Postgres logging
+
+Logging is not free.
+
+Each logged event adds:
+
+- CPU overhead
+- Disk IO
+- Additional load on log processing pipelines
+
+High-volume logging can amplify existing performance issues, especially under load.
+
+**Practical rules of thumb:**
+
+- Prefer slow-query logging over full statement logging
+- Increase logging temporarily during incidents
+- Validate logging changes in staging before production
+- Scale logging back down once the issue is resolved
+
+## How teams use Postgres logs in practice
+
+In real systems, Postgres logs are commonly used to:
+
+- Identify slow endpoints by spotting recurring slow queries
+- Investigate failed deployments or migrations
+- Diagnose connection storms and pool misconfigurations
+- Understand background activity like checkpoints or autovacuum
+- Correlate application errors with database-side failures
+
+They work best when paired with clear operational workflows and disciplined configuration changes.
+
+## Postgres logging best practices quick summary
+
+- Log slow queries, not everything
+- Always configure `log_line_prefix`
+- Prefer structured logs (`csvlog`) for analysis
+- Rotate and retain logs intentionally
+- Treat logging as a tuning tool, not a permanent dump
+
+## Final thoughts
+
+Postgres logs are one of the most powerful tools you have for understanding database behavior — but only if they’re configured with intent. Start minimal, focus on slow queries and errors, and increase verbosity only when you need answers.
+
+Good logging doesn’t mean more logs.
+It means **the right logs, at the right time, for the right questions**.