1 files changed, 73 insertions, 0 deletions
diff --git a/src/include/access/toast_compression.h b/src/include/access/toast_compression.h
new file mode 100644
index 0000000..c992ece
--- /dev/null
+++ b/src/include/access/toast_compression.h
@@ -0,0 +1,73 @@
+/*-------------------------------------------------------------------------
+ *
+ * toast_compression.h
+ *	  Functions for toast compression.
+ *
+ * Copyright (c) 2021, PostgreSQL Global Development Group
+ *
+ * src/include/access/toast_compression.h
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#ifndef TOAST_COMPRESSION_H
+#define TOAST_COMPRESSION_H
+
+/*
+ * GUC support.
+ *
+ * default_toast_compression is an integer for purposes of the GUC machinery,
+ * but the value is one of the char values defined below, as they appear in
+ * pg_attribute.attcompression, e.g. TOAST_PGLZ_COMPRESSION.
+ */
+extern int	default_toast_compression;
+
+/*
+ * Built-in compression method ID.  The toast compression header will store
+ * this in the first 2 bits of the raw length.  These built-in compression
+ * method IDs are directly mapped to the built-in compression methods.
+ *
+ * Don't use these values for anything other than understanding the meaning
+ * of the raw bits from a varlena; in particular, if the goal is to identify
+ * a compression method, use the constants TOAST_PGLZ_COMPRESSION, etc.
+ * below. We might someday support more than 4 compression methods, but
+ * we can never have more than 4 values in this enum, because there are
+ * only 2 bits available in the places where this is stored.
+ */
+typedef enum ToastCompressionId
+{
+	TOAST_PGLZ_COMPRESSION_ID = 0,
+	TOAST_LZ4_COMPRESSION_ID = 1,
+	TOAST_INVALID_COMPRESSION_ID = 2
+} ToastCompressionId;
+
+/*
+ * Built-in compression methods.  pg_attribute will store these in the
+ * attcompression column.  In attcompression, InvalidCompressionMethod
+ * denotes the default behavior.
+ */
+#define TOAST_PGLZ_COMPRESSION			'p'
+#define TOAST_LZ4_COMPRESSION			'l'
+#define InvalidCompressionMethod		'\0'
+
+#define CompressionMethodIsValid(cm)  ((cm) != InvalidCompressionMethod)
+
+
+/* pglz compression/decompression routines */
+extern struct varlena *pglz_compress_datum(const struct varlena *value);
+extern struct varlena *pglz_decompress_datum(const struct varlena *value);
+extern struct varlena *pglz_decompress_datum_slice(const struct varlena *value,
+												   int32 slicelength);
+
+/* lz4 compression/decompression routines */
+extern struct varlena *lz4_compress_datum(const struct varlena *value);
+extern struct varlena *lz4_decompress_datum(const struct varlena *value);
+extern struct varlena *lz4_decompress_datum_slice(const struct varlena *value,
+												  int32 slicelength);
+
+/* other stuff */
+extern ToastCompressionId toast_get_compression_id(struct varlena *attr);
+extern char CompressionNameToMethod(const char *compression);
+extern const char *GetCompressionMethodName(char method);
+
+#endif							/* TOAST_COMPRESSION_H */