Move pg_lzcompress.c to src/common.

The meta data of PGLZ symbolized by PGLZ_Header is removed, to make
the compression and decompression code independent on the backend-only
varlena facility. PGLZ_Header is being used to store some meta data
related to the data being compressed like the raw length of the uncompressed
record or some varlena-related data, making it unpluggable once PGLZ is
stored in src/common as it contains some backend-only code paths with
the management of varlena structures. The APIs of PGLZ are reworked
at the same time to do only compression and decompression of buffers
without the meta-data layer, simplifying its use for a more general usage.

On-disk format is preserved as well, so there is no incompatibility with
previous major versions of PostgreSQL for TOAST entries.

Exposing compression and decompression APIs of pglz makes possible its
use by extensions and contrib modules. Especially this commit is required
for upcoming WAL compression feature so that the WAL reader facility can
decompress the WAL data by using pglz_decompress.

Michael Paquier, reviewed by me.

1 files changed, 5 insertions, 26 deletions

diff --git a/src/include/utils/pg_lzcompress.h b/src/include/common/pg_lzcompress.h
index 4af24a32a4..52bcaf14b1 100644
--- a/src/include/utils/pg_lzcompress.h
+++ b/src/include/common/pg_lzcompress.h
@@ -3,7 +3,7 @@
  *
  *	Definitions for the builtin LZ compressor
  *
- * src/include/utils/pg_lzcompress.h
+ * src/include/common/pg_lzcompress.h
  * ----------
  */
 
@@ -12,35 +12,13 @@
 
 
 /* ----------
- * PGLZ_Header -
- *
- *		The information at the start of the compressed data.
- * ----------
- */
-typedef struct PGLZ_Header
-{
-	int32		vl_len_;		/* varlena header (do not touch directly!) */
-	int32		rawsize;
-} PGLZ_Header;
-
-
-/* ----------
  * 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 + sizeof(PGLZ_Header))
-
-/* ----------
- * PGLZ_RAW_SIZE -
- *
- *		Macro to determine the uncompressed data size contained
- *		in the entry.
- * ----------
- */
-#define PGLZ_RAW_SIZE(_lzdata)			((_lzdata)->rawsize)
+#define PGLZ_MAX_OUTPUT(_dlen)			((_dlen) + 4)
 
 
 /* ----------
@@ -105,8 +83,9 @@ extern const PGLZ_Strategy *const PGLZ_strategy_always;
  * Global function declarations
  * ----------
  */
-extern bool pglz_compress(const char *source, int32 slen, PGLZ_Header *dest,
+extern int32 pglz_compress(const char *source, int32 slen, char *dest,
 			  const PGLZ_Strategy *strategy);
-extern void pglz_decompress(const PGLZ_Header *source, char *dest);
+extern int32 pglz_decompress(const char *source, int32 slen, char *dest,
+			  int32 rawsize);
 
 #endif   /* _PG_LZCOMPRESS_H_ */