From the objective of OSS-DB Exam Gold
- Monitoring Performance - Access statistics
Sample Question
1.09
Select all the INCORRECT statements regarding pg_stat_database.
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Only one row of operational statistics for the entire database cluster is stored.
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"blks_hit" stores the number of blocks retrieved from the buffer cache (cache hits).
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"blks_read" is the sum of the number of blocks read from disk and the number of blocks read from the buffer cache.
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By default, the "track_counts" parameter is "off", so no activity statistics are collected.
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"tup_fetched" contains the number of rows fetched using index scans.
※This sample exam is different from those that appear in the actual OSS-DB Exam.
2025/05/30
Answer and Explanation
A. pg_stat_database contains one row of operational statistics per database.
B. This is a correct statement.
C. blks_read contains the number of blocks read from disk. It does not include the number of blocks read from the buffer cache.
D. The track_counts parameter must be on to collect activity statistics. By default, the track_counts parameter is on, so activity statistics are collected even immediately after initdb.
E. It contains the number of rows read, not just index scans. The number of rows read by index scans can be viewed table by table with idx_tup_fetch in pg_stat_(all|sys|user)_tables.
Therefore, the correct answers are A, C, D, and E.