Misconfiguration of autovacuum_vacuum_scale_factor in PostgreSQL can significantly impact database performance negatively. This parameter, along with autovacuum_vacuum_threshold, determines when the autovacuum process triggers for each table. Here's how incorrect settings can affect performance:

1. Set Too Low:
   • If autovacuum_vacuum_scale_factor is set too low, autovacuum may trigger too frequently. This can lead to unnecessary processing overhead, increased I/O activity, and potentially, reduced overall database performance due to frequent and possibly redundant vacuuming operations.
2. Set Too High:
   • On the other hand, setting this parameter too high can delay the vacuuming process. This delay can cause excessive table bloat, where dead tuples occupy space unnecessarily. Such bloat not only wastes disk space but also deteriorates the performance of queries and indexes as they have to process and navigate through a larger volume of data.
   • Delayed vacuuming can also lead to transaction ID wraparound issues, requiring aggressive vacuuming later that can lock tables and severely impact database availability and performance.
3. Impact on Query Planning:
   • Ineffective vacuuming due to misconfigured autovacuum_vacuum_scale_factor can result in outdated table statistics. The PostgreSQL query planner relies on these statistics to make decisions. Outdated stats can lead to inefficient query plans, thus adversely affecting query performance.

In summary, the autovacuum_vacuum_scale_factor needs to be carefully configured to strike a balance between preventing table bloat and avoiding excessive vacuuming overhead. The optimal setting often depends on the specific use case, data change rate, and database workload. Regular monitoring and adjustment are recommended to maintain optimal database performance.

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