Alvaro Herrera wrote:
> Per
> https://postgr.es/m/CAEepm=11ma_Z1HoPxPcSCANnh5ykHORa=hca1u1v1+5s_jw...@mail.gmail.com
> it seems that the dsm.c API is a bit inconvenient right now. I proposed
> in the first patch in that thread to change the API so that a segment is
> marked as "pinned" if created with no ResourceOwner set as current;
> which is essentially the same as creating a fake one, then marking the
> segment as pinned.
>
> Thomas agrees with me, so I propose this patch as preparatory work for
> the autovacuum/BRIN stuff I'm interested in.
Here's the proposed patch.
--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
>From ded46066cb634f7714706c8d347af2acf267da17 Mon Sep 17 00:00:00 2001
From: Alvaro Herrera <alvhe...@alvh.no-ip.org>
Date: Fri, 24 Mar 2017 19:27:22 -0300
Subject: [PATCH] Change dsm.c API so that mappings are pinned if created with
no resowner
---
src/backend/storage/ipc/dsm.c | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)
diff --git a/src/backend/storage/ipc/dsm.c b/src/backend/storage/ipc/dsm.c
index 54378bc..061a457 100644
--- a/src/backend/storage/ipc/dsm.c
+++ b/src/backend/storage/ipc/dsm.c
@@ -453,6 +453,11 @@ dsm_set_control_handle(dsm_handle h)
/*
* Create a new dynamic shared memory segment.
+ *
+ * If there is a CurrentResourceOwner, the new segment is born unpinned and the
+ * resource owner is in charge of destroying it (and will be blamed if it
+ * doesn't). If there's no current resource owner, then the segment starts in
+ * the pinned state, so it'll stay alive until explicitely unpinned.
*/
dsm_segment *
dsm_create(Size size, int flags)
@@ -1095,7 +1100,8 @@ dsm_create_descriptor(void)
{
dsm_segment *seg;
- ResourceOwnerEnlargeDSMs(CurrentResourceOwner);
+ if (CurrentResourceOwner)
+ ResourceOwnerEnlargeDSMs(CurrentResourceOwner);
seg = MemoryContextAlloc(TopMemoryContext, sizeof(dsm_segment));
dlist_push_head(&dsm_segment_list, &seg->node);
@@ -1106,8 +1112,11 @@ dsm_create_descriptor(void)
seg->mapped_address = NULL;
seg->mapped_size = 0;
- seg->resowner = CurrentResourceOwner;
- ResourceOwnerRememberDSM(CurrentResourceOwner, seg);
+ if (CurrentResourceOwner)
+ {
+ seg->resowner = CurrentResourceOwner;
+ ResourceOwnerRememberDSM(CurrentResourceOwner, seg);
+ }
slist_init(&seg->on_detach);
--
2.1.4
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