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Commit767bc02

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Allow DSM segments to be created as pinned
dsm_create and dsm_attach assumed that a current resource owner wasalways in place. Exploration with the API show that this isinconvenient: sometimes one must create a dummy resowner, create/attachthe DSM, only to pin the mapping later, which is wasteful. Changecreate/attach so that if there is no current resowner, the dsm iseffectively pinned right from the start.Discussion:https://postgr.es/m/20170324232710.32acsfsvjqfgc6ud@alvherre.pgsqlReviewed by Thomas Munro.
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  • src/backend/storage/ipc

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‎src/backend/storage/ipc/dsm.c

Lines changed: 16 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -453,6 +453,13 @@ dsm_set_control_handle(dsm_handle h)
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/*
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* Create a new dynamic shared memory segment.
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*
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* If there is a non-NULL CurrentResourceOwner, the new segment is associated
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* with it and must be detached before the resource owner releases, or a
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* warning will be logged. If CurrentResourceOwner is NULL, the segment
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* remains attached until explicitely detached or the session ends.
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* Creating with a NULL CurrentResourceOwner is equivalent to creating
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* with a non-NULL CurrentResourceOwner and then calling dsm_pin_mapping.
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*/
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dsm_segment*
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dsm_create(Sizesize,intflags)
@@ -544,6 +551,11 @@ dsm_create(Size size, int flags)
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* This can happen if we're asked to attach the segment, but then everyone
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* else detaches it (causing it to be destroyed) before we get around to
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* attaching it.
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*
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* If there is a non-NULL CurrentResourceOwner, the attached segment is
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* associated with it and must be detached before the resource owner releases,
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* or a warning will be logged. Otherwise the segment remains attached until
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* explicitely detached or the session ends. See the note atop dsm_create().
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*/
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dsm_segment*
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dsm_attach(dsm_handleh)
@@ -1095,7 +1107,8 @@ dsm_create_descriptor(void)
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{
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dsm_segment*seg;
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1098-
ResourceOwnerEnlargeDSMs(CurrentResourceOwner);
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if (CurrentResourceOwner)
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ResourceOwnerEnlargeDSMs(CurrentResourceOwner);
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seg=MemoryContextAlloc(TopMemoryContext,sizeof(dsm_segment));
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dlist_push_head(&dsm_segment_list,&seg->node);
@@ -1107,7 +1120,8 @@ dsm_create_descriptor(void)
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seg->mapped_size=0;
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seg->resowner=CurrentResourceOwner;
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ResourceOwnerRememberDSM(CurrentResourceOwner,seg);
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if (CurrentResourceOwner)
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ResourceOwnerRememberDSM(CurrentResourceOwner,seg);
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slist_init(&seg->on_detach);
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