1 files changed, 53 insertions, 0 deletions
diff --git a/src/include/replication/walprotocol.h b/src/include/replication/walprotocol.h
new file mode 100644
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+++ b/src/include/replication/walprotocol.h
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+/*-------------------------------------------------------------------------
+ *
+ * walprotocol.h
+ *	  Definitions relevant to the streaming WAL transmission protocol.
+ *
+ * Portions Copyright (c) 2010-2010, PostgreSQL Global Development Group
+ *
+ * $PostgreSQL: pgsql/src/include/replication/walprotocol.h,v 1.1 2010/06/03 22:17:32 tgl Exp $
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef _WALPROTOCOL_H
+#define _WALPROTOCOL_H
+
+#include "access/xlogdefs.h"
+#include "utils/timestamp.h"
+
+
+/*
+ * Header for a WAL data message (message type 'w').  This is wrapped within
+ * a CopyData message at the FE/BE protocol level.
+ *
+ * The header is followed by actual WAL data.  Note that the data length is
+ * not specified in the header --- it's just whatever remains in the message.
+ *
+ * walEnd and sendTime are not essential data, but are provided in case
+ * the receiver wants to adjust its behavior depending on how far behind
+ * it is.
+ */
+typedef struct
+{
+	/* WAL start location of the data included in this message */
+	XLogRecPtr	dataStart;
+
+	/* Current end of WAL on the sender */
+	XLogRecPtr	walEnd;
+
+	/* Sender's system clock at the time of transmission */
+	TimestampTz	sendTime;
+} WalDataMessageHeader;
+
+/*
+ * Maximum data payload in a WAL data message.  Must be >= XLOG_BLCKSZ.
+ *
+ * We don't have a good idea of what a good value would be; there's some
+ * overhead per message in both walsender and walreceiver, but on the other
+ * hand sending large batches makes walsender less responsive to signals
+ * because signals are checked only between messages.  128kB (with
+ * default 8k blocks) seems like a reasonable guess for now.
+ */
+#define MAX_SEND_SIZE (XLOG_BLCKSZ * 16)
+
+#endif   /* _WALPROTOCOL_H */