The new LZ compression and an lztext data type based on it.

Jan

1 files changed, 125 insertions, 0 deletions

diff --git a/src/include/utils/pg_lzcompress.h b/src/include/utils/pg_lzcompress.h
new file mode 100644
index 00000000000..dba52fa5888
--- /dev/null
+++ b/src/include/utils/pg_lzcompress.h
@@ -0,0 +1,125 @@
+/* ----------
+ * pg_lzcompress.h -
+ *
+ * $Header: /cvsroot/pgsql/src/include/utils/pg_lzcompress.h,v 1.1 1999/11/17 21:21:51 wieck Exp $
+ *
+ *	Definitions for the builtin LZ compressor
+ * ----------
+ */
+
+#ifndef _PG_LZCOMPRESS_H_
+#define _PG_LZCOMPRESS_H_
+
+
+/* ----------
+ * PGLZ_Header -
+ *
+ *      The information at the top of the compressed data.
+ *		The varsize must be kept the same data type as the value
+ *		in front of all variable size data types in PostgreSQL.
+ * ----------
+ */
+typedef struct PGLZ_Header {
+    int32                       varsize;
+    int32                       rawsize;
+} PGLZ_Header;
+
+
+/* ----------
+ * PGLZ_MAX_OUTPUT -
+ *
+ *		Macro to compute the maximum buffer required for the
+ *		compression output. It is larger than the input, because
+ *		in the worst case, we cannot write out one single tag but
+ *		need one control byte per 8 literal data bytes plus the
+ *		EOF mark at the end.
+ * ----------
+ */
+#define PGLZ_MAX_OUTPUT(_dlen)			((_dlen) + (((_dlen) | 0x07) >> 3)	\
+													 + sizeof(PGLZ_Header))
+#define PGLZ_RAW_SIZE(_lzdata)			(_lzdata->rawsize)
+#define PGLZ_IS_COMPRESSED(_lzdata)		(_lzdata->varsize != 				\
+										 _lzdata->rawsize + sizeof(PGLZ_Header))
+
+/* ----------
+ * PGLZ_Strategy -
+ *
+ *		Some values that control the compression algorithm.
+ *
+ *		min_input_size		Minimum input data size to start compression.
+ *
+ *		force_input_size	Input data size at which compressed storage is
+ *							forced even if the compression rate drops below
+ *							min_comp_rate (but not below 0).
+ *
+ *		min_comp_rate		Minimum compression rate (0-99%), the output
+ *							must be smaller than the input. If that isn't
+ *							the case, the compressor will throw away it's
+ *							output and copy the original, uncompressed data
+ *							to the output buffer.
+ *
+ *		match_size_good		The initial GOOD match size when starting history
+ *							lookup. When looking up the history to find a
+ *							match that could be expressed as a tag, the
+ *							algorithm does not allways walk back entirely.
+ *							A good match fast is usually better than the 
+ *							best possible one very late. For each iteration
+ *							in the lookup, this value is lowered so the
+ *							longer the lookup takes, the smaller matches
+ *							are considered good.
+ *
+ *		match_size_drop		The percentage, match_size_good is lowered
+ *							at each history check. Allowed values are
+ *							0 (no change until end) to 100 (only check
+ *							latest history entry at all).
+ * ----------
+ */
+typedef struct PGLZ_Strategy {
+	int32		min_input_size;
+	int32		force_input_size;
+	int32		min_comp_rate;
+	int32		match_size_good;
+	int32		match_size_drop;
+} PGLZ_Strategy;
+
+
+/* ----------
+ * The standard strategies
+ *
+ *		PGLZ_strategy_default		Starts compression only if input is
+ *									at least 256 bytes large. Stores output
+ *									uncompressed if compression does not
+ *									gain at least 20% size reducture but
+ *									input does not exceed 6K. Stops history
+ *									lookup if at least a 128 byte long
+ *									match has been found.
+ *
+ *									This is the default strategy if none
+ *									is given to pglz_compress().
+ *
+ *		PGLZ_strategy_allways		Starts compression on any infinitely
+ *									small input and does fallback to
+ *									uncompressed storage only if output
+ *									would be larger than input.
+ *
+ *		PGLZ_strategy_never			Force pglz_compress to act as a custom
+ *									interface for memcpy(). Only useful
+ *									for generic interfacing.
+ * ----------
+ */
+extern PGLZ_Strategy	*PGLZ_strategy_default;
+extern PGLZ_Strategy	*PGLZ_strategy_allways;
+extern PGLZ_Strategy	*PGLZ_strategy_never;
+
+
+/* ----------
+ * Global function declarations
+ * ----------
+ */
+int	pglz_compress (char *source, int32 slen, PGLZ_Header *dest,
+									 PGLZ_Strategy *strategy);
+int pglz_decompress (PGLZ_Header *source, char *dest);
+
+
+#endif /* _PG_LZCOMPRESS_H_ */
+