EVOLUTION-NINJA

Edit File: pg_lzcompress.h

/* ---------- * pg_lzcompress.h - * * Definitions for the builtin LZ compressor * * src/include/utils/pg_lzcompress.h * ---------- */ #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_ */