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db_include/common/pg_lzcompress.h

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+/* ----------
+ * pg_lzcompress.h -
+ *
+ *	Definitions for the builtin LZ compressor
+ *
+ * src/include/common/pg_lzcompress.h
+ * ----------
+ */
+
+#ifndef _PG_LZCOMPRESS_H_
+#define _PG_LZCOMPRESS_H_
+
+
+/* ----------
+ * PGLZ_MAX_OUTPUT -
+ *
+ *		Macro to compute the buffer size required by pglz_compress().
+ *		We allow 4 bytes for overrun before detecting compression failure.
+ * ----------
+ */
+#define PGLZ_MAX_OUTPUT(_dlen)			((_dlen) + 4)
+
+
+/* ----------
+ * PGLZ_Strategy -
+ *
+ *		Some values that control the compression algorithm.
+ *
+ *		min_input_size		Minimum input data size to consider compression.
+ *
+ *		max_input_size		Maximum input data size to consider compression.
+ *
+ *		min_comp_rate		Minimum compression rate (0-99%) to require.
+ *							Regardless of min_comp_rate, the output must be
+ *							smaller than the input, else we don't store
+ *							compressed.
+ *
+ *		first_success_by	Abandon compression if we find no compressible
+ *							data within the first this-many bytes.
+ *
+ *		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 always 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 by which match_size_good is lowered
+ *							after 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		max_input_size;
+	int32		min_comp_rate;
+	int32		first_success_by;
+	int32		match_size_good;
+	int32		match_size_drop;
+} PGLZ_Strategy;
+
+
+/* ----------
+ * The standard strategies
+ *
+ *		PGLZ_strategy_default		Recommended default strategy for TOAST.
+ *
+ *		PGLZ_strategy_always		Try to compress inputs of any length.
+ *									Fallback to uncompressed storage only if
+ *									output would be larger than input.
+ * ----------
+ */
+extern const PGLZ_Strategy *const PGLZ_strategy_default;
+extern const PGLZ_Strategy *const PGLZ_strategy_always;
+
+
+/* ----------
+ * Global function declarations
+ * ----------
+ */
+extern int32 pglz_compress(const char *source, int32 slen, char *dest,
+						   const PGLZ_Strategy *strategy);
+extern int32 pglz_decompress(const char *source, int32 slen, char *dest,
+							 int32 rawsize, bool check_complete);
+extern int32 pglz_maximum_compressed_size(int32 rawsize,
+										  int32 total_compressed_size);
+
+#endif							/* _PG_LZCOMPRESS_H_ */