Hi Hackers, When a subscription has retain_dead_tuples enabled with maxretention set to zero (unlimited retention), adjust_xid_advance_interval() caps xid_advance_interval to Min(interval, maxretention). Since maxretention is zero, this always collapses the interval to zero milliseconds.
A zero makes TimestampDifferenceExceeds(last_time, now, 0) always true in get_candidate_xid(). This causes the apply worker to call GetOldestActiveTransactionId() on every single WAL message. This results in a huge number of ProcArrayLock acquisitions under moderate write load. Fix by adding a maxretention > 0 guard to the cap. When maxretention is zero , the exponential back-off in adjust_xid_advance_interval() now works correctly, growing the interval from 100 ms toward the 180 s ceiling. Measured with perf uprobe counting GetOldestActiveTransactionId calls at ~39K TPS (pgbench, 5 clients): Before fix: 25,104 calls / 5 s (~5,021/s) After fix: 31 calls / 5 s (~6/s) Thank Satya
0001-Fix-apply-worker-busy-loop-when-subscription-max_ret.patch
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