From: Teodor Sigaev <teodor@sigaev.ru>
Date: Mon, 20 Mar 2017 15:48:46 +0000 (+0300)
Subject: Revert unintentional change in increasing usage count during pin of buffers,
X-Git-Tag: REL_10_BETA1~591
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=9cf6033281fdaf938b826545a643f951086d8671;p=postgresql

Revert unintentional change in increasing usage count during pin of buffers,
this makes buffer access strategy have no effect.
Change was a part of commit 48354581a49c30f5757c203415aa8412d85b0f70 during 9.6
release cycle, so backpath to 9.6

Reported-by: Jim Nasby
Author: Alexander Korotkov
Reviewed-by: Jim Nasby, Andres Freund

https://commitfest.postgresql.org/13/1029/
---

diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 2ca2ab9753..2109cbf858 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -1595,9 +1595,21 @@ PinBuffer(BufferDesc *buf, BufferAccessStrategy strategy)
 			/* increase refcount */
 			buf_state += BUF_REFCOUNT_ONE;
 
-			/* increase usagecount unless already max */
-			if (BUF_STATE_GET_USAGECOUNT(buf_state) != BM_MAX_USAGE_COUNT)
-				buf_state += BUF_USAGECOUNT_ONE;
+			if (strategy == NULL)
+			{
+				/* Default case: increase usagecount unless already max. */
+				if (BUF_STATE_GET_USAGECOUNT(buf_state) < BM_MAX_USAGE_COUNT)
+					buf_state += BUF_USAGECOUNT_ONE;
+			}
+			else
+			{
+				/*
+				 * Ring buffers shouldn't evict others from pool.  Thus we
+				 * don't make usagecount more than 1.
+				 */
+				if (BUF_STATE_GET_USAGECOUNT(buf_state) == 0)
+					buf_state += BUF_USAGECOUNT_ONE;
+			}
 
 			if (pg_atomic_compare_exchange_u32(&buf->state, &old_buf_state,
 											   buf_state))