| /* ---------- | |
| * pg_lzcompress.h - | |
| * | |
| * Definitions for the builtin LZ compressor | |
| * | |
| * src/include/common/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. | |
| * ---------- | |
| */ | |
| /* ---------- | |
| * 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 PGDLLIMPORT const PGLZ_Strategy *const PGLZ_strategy_default; | |
| extern PGDLLIMPORT 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); | |