PCA PCA Storage & Retention 3

Question 1

What file format do Prometheus TSDB chunk files use?

Accepted Answer

A custom binary format optimized for time-series compression

Answer

Prometheus TSDB uses a custom binary chunk format with delta-of-delta and XOR compression for timestamps and values.

Question 2

What happens to the WAL when Prometheus shuts down cleanly?

Accepted Answer

It is checkpointed so replay on restart is faster

Answer

On a clean shutdown, Prometheus creates a WAL checkpoint that truncates fully-compacted segments, speeding up the next startup.

Question 3

Which Prometheus command-line flag specifies the directory where TSDB data is stored?

Accepted Answer

--storage.tsdb.path

Answer

The --storage.tsdb.path flag sets the directory where Prometheus writes all its TSDB blocks and WAL.

Question 4

What is the purpose of the `meta.json` file inside a Prometheus TSDB block directory?

Accepted Answer

It stores the block's time range, version, statistics, and compaction history

Answer

meta.json is the block's manifest, recording its min/max time, ULID, number of series, and compaction ancestry.

Question 5

Why might setting a very short TSDB retention period cause high disk I/O in Prometheus?

Accepted Answer

Frequent block deletions and compactions run more often to purge data quickly

Answer

Short retention causes Prometheus to compact and delete blocks more frequently, increasing background disk activity.

(PCA) Prometheus Certified Associate Practice Test