blob: e81ae0d5ca7f3836f0fe8094131af36326aa656f (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
|
/* ----------
* pg_lzcompress.h -
*
* Definitions for the builtin LZ compressor
*
* $PostgreSQL: pgsql/src/include/utils/pg_lzcompress.h,v 1.17 2008/03/07 23:20:21 tgl Exp $
* ----------
*/
#ifndef _PG_LZCOMPRESS_H_
#define _PG_LZCOMPRESS_H_
/* ----------
* 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)
/* ----------
* 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 bool pglz_compress(const char *source, int32 slen, PGLZ_Header *dest,
const PGLZ_Strategy *strategy);
extern void pglz_decompress(const PGLZ_Header *source, char *dest);
#endif /* _PG_LZCOMPRESS_H_ */
|
