Update description of spilled counters in pg_stat_replication_slots view.
This is to make the description of spilled counters clear.
Author: Amit Kapila
Discussion:
@@ -2603,9 +2603,9 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
</para>
<para>
Number of transactions spilled to disk after the memory used by
- logical decoding exceeds <literal>logical_decoding_work_mem</literal>. The
- counter gets incremented both for toplevel transactions and
- subtransactions.
+ logical decoding of changes from WAL for this slot exceeds
+ <literal>logical_decoding_work_mem</literal>. The counter gets
+ incremented both for toplevel transactions and subtransactions.
</para></entry>
</row>
@@ -2614,7 +2614,8 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
<structfield>spill_count</structfield> <type>bigint</type>
</para>
<para>
- Number of times transactions were spilled to disk. Transactions
+ Number of times transactions were spilled to disk while performing
+ decoding of changes from WAL for this slot. Transactions
may get spilled repeatedly, and this counter gets incremented on every
such invocation.
</para></entry>
@@ -2625,7 +2626,10 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
<structfield>spill_bytes</structfield> <type>bigint</type>
</para>
<para>
- Amount of decoded transaction data spilled to disk.
+ Amount of decoded transaction data spilled to disk while performing
+ decoding of changes from WAL for this slot. This and other spill
+ counters can be used to gauge the I/O occurred during logical decoding
+ and accordingly can tune <literal>logical_decoding_work_mem</literal>.
</para></entry>
</row>
