From cc5f81366c36b3dd8f02bd9be1cf75b2cc8482bd Mon Sep 17 00:00:00 2001
From: Andres Freund
Date: Thu, 14 Sep 2017 19:59:21 -0700
Subject: Add support for coordinating record typmods among parallel workers.

Tuples can have type RECORDOID and a typmod number that identifies a blessed
TupleDesc in a backend-private cache.  To support the sharing of such tuples
through shared memory and temporary files, provide a typmod registry in
shared memory.

To achieve that, introduce per-session DSM segments, created on demand when a
backend first runs a parallel query.  The per-session DSM segment has a
table-of-contents just like the per-query DSM segment, and initially the
contents are a shared record typmod registry and a DSA area to provide the
space it needs to grow.

State relating to the current session is accessed via a Session object
reached through global variable CurrentSession that may require significant
redesign further down the road as we figure out what else needs to be shared
or remodelled.

Author: Thomas Munro
Reviewed-By: Andres Freund
Discussion: https://postgr.es/m/CAEepm=0ZtQ-SpsgCyzzYpsXS6e=kZWqk3g5Ygn3MDV7A8dabUA@mail.gmail.com
---
 src/include/access/session.h | 44 ++++++++++++++++++++++++++++++++++++++++++++
 src/include/access/tupdesc.h |  6 ++++++
 src/include/storage/lwlock.h |  3 +++
 src/include/utils/typcache.h | 10 ++++++++++
 4 files changed, 63 insertions(+)
 create mode 100644 src/include/access/session.h

(limited to 'src/include')

diff --git a/src/include/access/session.h b/src/include/access/session.h
new file mode 100644
index 00000000000..8376dc53127
--- /dev/null
+++ b/src/include/access/session.h
@@ -0,0 +1,44 @@
+/*-------------------------------------------------------------------------
+ *
+ * session.h
+ *	  Encapsulation of user session.
+ *
+ * Copyright (c) 2017, PostgreSQL Global Development Group
+ *
+ * src/include/access/session.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef SESSION_H
+#define SESSION_H
+
+#include "lib/dshash.h"
+
+/* Defined in typcache.c */
+typedef struct SharedRecordTypmodRegistry SharedRecordTypmodRegistry;
+
+/*
+ * A struct encapsulating some elements of a user's session.  For now this
+ * manages state that applies to parallel query, but it principle it could
+ * include other things that are currently global variables.
+ */
+typedef struct Session
+{
+	dsm_segment *segment;		/* The session-scoped DSM segment. */
+	dsa_area   *area;			/* The session-scoped DSA area. */
+
+	/* State managed by typcache.c. */
+	SharedRecordTypmodRegistry *shared_typmod_registry;
+	dshash_table *shared_record_table;
+	dshash_table *shared_typmod_table;
+} Session;
+
+extern void InitializeSession(void);
+extern dsm_handle GetSessionDsmHandle(void);
+extern void AttachSession(dsm_handle handle);
+extern void DetachSession(void);
+
+/* The current session, or NULL for none. */
+extern Session *CurrentSession;
+
+#endif							/* SESSION_H */
diff --git a/src/include/access/tupdesc.h b/src/include/access/tupdesc.h
index 989fe738bbe..c15610e7679 100644
--- a/src/include/access/tupdesc.h
+++ b/src/include/access/tupdesc.h
@@ -92,6 +92,12 @@ extern TupleDesc CreateTupleDescCopy(TupleDesc tupdesc);
 
 extern TupleDesc CreateTupleDescCopyConstr(TupleDesc tupdesc);
 
+#define TupleDescSize(src) \
+	(offsetof(struct tupleDesc, attrs) + \
+	 (src)->natts * sizeof(FormData_pg_attribute))
+
+extern void TupleDescCopy(TupleDesc dst, TupleDesc src);
+
 extern void TupleDescCopyEntry(TupleDesc dst, AttrNumber dstAttno,
 				   TupleDesc src, AttrNumber srcAttno);
 
diff --git a/src/include/storage/lwlock.h b/src/include/storage/lwlock.h
index 3d16132c88f..f4c4aed7f91 100644
--- a/src/include/storage/lwlock.h
+++ b/src/include/storage/lwlock.h
@@ -212,6 +212,9 @@ typedef enum BuiltinTrancheIds
 	LWTRANCHE_LOCK_MANAGER,
 	LWTRANCHE_PREDICATE_LOCK_MANAGER,
 	LWTRANCHE_PARALLEL_QUERY_DSA,
+	LWTRANCHE_SESSION_DSA,
+	LWTRANCHE_SESSION_RECORD_TABLE,
+	LWTRANCHE_SESSION_TYPMOD_TABLE,
 	LWTRANCHE_TBM,
 	LWTRANCHE_FIRST_USER_DEFINED
 }			BuiltinTrancheIds;
diff --git a/src/include/utils/typcache.h b/src/include/utils/typcache.h
index b4f75921625..41b645a58f8 100644
--- a/src/include/utils/typcache.h
+++ b/src/include/utils/typcache.h
@@ -18,6 +18,8 @@
 
 #include "access/tupdesc.h"
 #include "fmgr.h"
+#include "storage/dsm.h"
+#include "utils/dsa.h"
 
 
 /* DomainConstraintCache is an opaque struct known only within typcache.c */
@@ -143,6 +145,7 @@ typedef struct DomainConstraintRef
 	MemoryContextCallback callback; /* used to release refcount when done */
 } DomainConstraintRef;
 
+typedef struct SharedRecordTypmodRegistry SharedRecordTypmodRegistry;
 
 extern TypeCacheEntry *lookup_type_cache(Oid type_id, int flags);
 
@@ -164,4 +167,11 @@ extern void assign_record_type_typmod(TupleDesc tupDesc);
 
 extern int	compare_values_of_enum(TypeCacheEntry *tcache, Oid arg1, Oid arg2);
 
+extern size_t SharedRecordTypmodRegistryEstimate(void);
+
+extern void SharedRecordTypmodRegistryInit(SharedRecordTypmodRegistry *,
+							   dsm_segment *segment, dsa_area *area);
+
+extern void SharedRecordTypmodRegistryAttach(SharedRecordTypmodRegistry *);
+
 #endif							/* TYPCACHE_H */
-- 
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