1 files changed, 82 insertions, 0 deletions
diff --git a/src/include/access/xlogprefetch.h b/src/include/access/xlogprefetch.h
new file mode 100644
index 00000000000..59ce9c64739
--- /dev/null
+++ b/src/include/access/xlogprefetch.h
@@ -0,0 +1,82 @@
+/*-------------------------------------------------------------------------
+ *
+ * xlogprefetch.h
+ *		Declarations for the recovery prefetching module.
+ *
+ * Portions Copyright (c) 2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *		src/include/access/xlogprefetch.h
+ *-------------------------------------------------------------------------
+ */
+#ifndef XLOGPREFETCH_H
+#define XLOGPREFETCH_H
+
+#include "access/xlogdefs.h"
+
+/* GUCs */
+extern bool recovery_prefetch;
+extern bool recovery_prefetch_fpw;
+
+struct XLogPrefetcher;
+typedef struct XLogPrefetcher XLogPrefetcher;
+
+extern int	XLogPrefetchReconfigureCount;
+
+typedef struct XLogPrefetchState
+{
+	XLogReaderState *reader;
+	XLogPrefetcher *prefetcher;
+	int			reconfigure_count;
+} XLogPrefetchState;
+
+extern size_t XLogPrefetchShmemSize(void);
+extern void XLogPrefetchShmemInit(void);
+
+extern void XLogPrefetchReconfigure(void);
+extern void XLogPrefetchRequestResetStats(void);
+
+extern void XLogPrefetchBegin(XLogPrefetchState *state, XLogReaderState *reader);
+extern void XLogPrefetchEnd(XLogPrefetchState *state);
+
+/* Functions exposed only for the use of XLogPrefetch(). */
+extern XLogPrefetcher *XLogPrefetcherAllocate(XLogReaderState *reader);
+extern void XLogPrefetcherFree(XLogPrefetcher *prefetcher);
+extern bool XLogPrefetcherReadAhead(XLogPrefetcher *prefetch,
+									XLogRecPtr replaying_lsn);
+
+/*
+ * Tell the prefetching module that we are now replaying a given LSN, so that
+ * it can decide how far ahead to read in the WAL, if configured.  Return
+ * true if more data is needed by the reader.
+ */
+static inline bool
+XLogPrefetch(XLogPrefetchState *state, XLogRecPtr replaying_lsn)
+{
+	/*
+	 * Handle any configuration changes.  Rather than trying to deal with
+	 * various parameter changes, we just tear down and set up a new
+	 * prefetcher if anything we depend on changes.
+	 */
+	if (unlikely(state->reconfigure_count != XLogPrefetchReconfigureCount))
+	{
+		/* If we had a prefetcher, tear it down. */
+		if (state->prefetcher)
+		{
+			XLogPrefetcherFree(state->prefetcher);
+			state->prefetcher = NULL;
+		}
+		/* If we want a prefetcher, set it up. */
+		if (recovery_prefetch)
+			state->prefetcher = XLogPrefetcherAllocate(state->reader);
+		state->reconfigure_count = XLogPrefetchReconfigureCount;
+	}
+
+	if (state->prefetcher)
+		return XLogPrefetcherReadAhead(state->prefetcher, replaying_lsn);
+
+	return false;
+}
+
+#endif