1 files changed, 186 insertions, 0 deletions
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
new file mode 100644
index 0000000..0057443
--- /dev/null
+++ b/src/backend/storage/buffer/buf_init.c
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+/*-------------------------------------------------------------------------
+ *
+ * buf_init.c
+ *	  buffer manager initialization routines
+ *
+ * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/storage/buffer/buf_init.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "storage/buf_internals.h"
+#include "storage/bufmgr.h"
+#include "storage/proc.h"
+
+BufferDescPadded *BufferDescriptors;
+char	   *BufferBlocks;
+ConditionVariableMinimallyPadded *BufferIOCVArray;
+WritebackContext BackendWritebackContext;
+CkptSortItem *CkptBufferIds;
+
+
+/*
+ * Data Structures:
+ *		buffers live in a freelist and a lookup data structure.
+ *
+ *
+ * Buffer Lookup:
+ *		Two important notes.  First, the buffer has to be
+ *		available for lookup BEFORE an IO begins.  Otherwise
+ *		a second process trying to read the buffer will
+ *		allocate its own copy and the buffer pool will
+ *		become inconsistent.
+ *
+ * Buffer Replacement:
+ *		see freelist.c.  A buffer cannot be replaced while in
+ *		use either by data manager or during IO.
+ *
+ *
+ * Synchronization/Locking:
+ *
+ * IO_IN_PROGRESS -- this is a flag in the buffer descriptor.
+ *		It must be set when an IO is initiated and cleared at
+ *		the end of the IO.  It is there to make sure that one
+ *		process doesn't start to use a buffer while another is
+ *		faulting it in.  see WaitIO and related routines.
+ *
+ * refcount --	Counts the number of processes holding pins on a buffer.
+ *		A buffer is pinned during IO and immediately after a BufferAlloc().
+ *		Pins must be released before end of transaction.  For efficiency the
+ *		shared refcount isn't increased if an individual backend pins a buffer
+ *		multiple times. Check the PrivateRefCount infrastructure in bufmgr.c.
+ */
+
+
+/*
+ * Initialize shared buffer pool
+ *
+ * This is called once during shared-memory initialization (either in the
+ * postmaster, or in a standalone backend).
+ */
+void
+InitBufferPool(void)
+{
+	bool		foundBufs,
+				foundDescs,
+				foundIOCV,
+				foundBufCkpt;
+
+	/* Align descriptors to a cacheline boundary. */
+	BufferDescriptors = (BufferDescPadded *)
+		ShmemInitStruct("Buffer Descriptors",
+						NBuffers * sizeof(BufferDescPadded),
+						&foundDescs);
+
+	/* Align buffer pool on IO page size boundary. */
+	BufferBlocks = (char *)
+		TYPEALIGN(PG_IO_ALIGN_SIZE,
+				  ShmemInitStruct("Buffer Blocks",
+								  NBuffers * (Size) BLCKSZ + PG_IO_ALIGN_SIZE,
+								  &foundBufs));
+
+	/* Align condition variables to cacheline boundary. */
+	BufferIOCVArray = (ConditionVariableMinimallyPadded *)
+		ShmemInitStruct("Buffer IO Condition Variables",
+						NBuffers * sizeof(ConditionVariableMinimallyPadded),
+						&foundIOCV);
+
+	/*
+	 * The array used to sort to-be-checkpointed buffer ids is located in
+	 * shared memory, to avoid having to allocate significant amounts of
+	 * memory at runtime. As that'd be in the middle of a checkpoint, or when
+	 * the checkpointer is restarted, memory allocation failures would be
+	 * painful.
+	 */
+	CkptBufferIds = (CkptSortItem *)
+		ShmemInitStruct("Checkpoint BufferIds",
+						NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
+
+	if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
+	{
+		/* should find all of these, or none of them */
+		Assert(foundDescs && foundBufs && foundIOCV && foundBufCkpt);
+		/* note: this path is only taken in EXEC_BACKEND case */
+	}
+	else
+	{
+		int			i;
+
+		/*
+		 * Initialize all the buffer headers.
+		 */
+		for (i = 0; i < NBuffers; i++)
+		{
+			BufferDesc *buf = GetBufferDescriptor(i);
+
+			ClearBufferTag(&buf->tag);
+
+			pg_atomic_init_u32(&buf->state, 0);
+			buf->wait_backend_pgprocno = INVALID_PGPROCNO;
+
+			buf->buf_id = i;
+
+			/*
+			 * Initially link all the buffers together as unused. Subsequent
+			 * management of this list is done by freelist.c.
+			 */
+			buf->freeNext = i + 1;
+
+			LWLockInitialize(BufferDescriptorGetContentLock(buf),
+							 LWTRANCHE_BUFFER_CONTENT);
+
+			ConditionVariableInit(BufferDescriptorGetIOCV(buf));
+		}
+
+		/* Correct last entry of linked list */
+		GetBufferDescriptor(NBuffers - 1)->freeNext = FREENEXT_END_OF_LIST;
+	}
+
+	/* Init other shared buffer-management stuff */
+	StrategyInitialize(!foundDescs);
+
+	/* Initialize per-backend file flush context */
+	WritebackContextInit(&BackendWritebackContext,
+						 &backend_flush_after);
+}
+
+/*
+ * BufferShmemSize
+ *
+ * compute the size of shared memory for the buffer pool including
+ * data pages, buffer descriptors, hash tables, etc.
+ */
+Size
+BufferShmemSize(void)
+{
+	Size		size = 0;
+
+	/* size of buffer descriptors */
+	size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
+	/* to allow aligning buffer descriptors */
+	size = add_size(size, PG_CACHE_LINE_SIZE);
+
+	/* size of data pages, plus alignment padding */
+	size = add_size(size, PG_IO_ALIGN_SIZE);
+	size = add_size(size, mul_size(NBuffers, BLCKSZ));
+
+	/* size of stuff controlled by freelist.c */
+	size = add_size(size, StrategyShmemSize());
+
+	/* size of I/O condition variables */
+	size = add_size(size, mul_size(NBuffers,
+								   sizeof(ConditionVariableMinimallyPadded)));
+	/* to allow aligning the above */
+	size = add_size(size, PG_CACHE_LINE_SIZE);
+
+	/* size of checkpoint sort array in bufmgr.c */
+	size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
+
+	return size;
+}