diff options
Diffstat (limited to 'src/include/utils/pg_lzcompress.h')
| -rw-r--r-- | src/include/utils/pg_lzcompress.h | 45 |
1 files changed, 17 insertions, 28 deletions
diff --git a/src/include/utils/pg_lzcompress.h b/src/include/utils/pg_lzcompress.h index a3c49ae7a72..e81ae0d5ca7 100644 --- a/src/include/utils/pg_lzcompress.h +++ b/src/include/utils/pg_lzcompress.h @@ -3,7 +3,7 @@ * * Definitions for the builtin LZ compressor * - * $PostgreSQL: pgsql/src/include/utils/pg_lzcompress.h,v 1.16 2007/11/15 21:14:45 momjian Exp $ + * $PostgreSQL: pgsql/src/include/utils/pg_lzcompress.h,v 1.17 2008/03/07 23:20:21 tgl Exp $ * ---------- */ @@ -14,7 +14,7 @@ /* ---------- * PGLZ_Header - * - * The information at the top of the compressed data. + * The information at the start of the compressed data. * ---------- */ typedef struct PGLZ_Header @@ -48,19 +48,17 @@ typedef struct PGLZ_Header * * Some values that control the compression algorithm. * - * min_input_size Minimum input data size to start compression. + * min_input_size Minimum input data size to consider compression. * - * force_input_size Minimum input data size to force compression - * even if the compression rate drops below - * min_comp_rate. But in any case the output - * must be smaller than the input. If that isn't - * the case, the compressor will throw away its - * output and copy the original, uncompressed data - * to the output buffer. + * max_input_size Maximum input data size to consider compression. * - * min_comp_rate Minimum compression rate (0-99%) to require for - * inputs smaller than force_input_size. If not - * achieved, the output will be uncompressed. + * 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 @@ -81,8 +79,9 @@ typedef struct PGLZ_Header typedef struct PGLZ_Strategy { int32 min_input_size; - int32 force_input_size; + int32 max_input_size; int32 min_comp_rate; + int32 first_success_by; int32 match_size_good; int32 match_size_drop; } PGLZ_Strategy; @@ -91,21 +90,11 @@ typedef struct PGLZ_Strategy /* ---------- * The standard strategies * - * PGLZ_strategy_default Starts compression only if input is - * at least 256 bytes large. Stores output - * uncompressed if compression does not - * gain at least 20% size reducture but - * input does not exceed 6K. Stops history - * lookup if at least a 128 byte long - * match has been found. - * - * This is the default strategy if none - * is given to pglz_compress(). + * PGLZ_strategy_default Recommended default strategy for TOAST. * - * PGLZ_strategy_always Starts compression on any infinitely - * small input and does fallback to - * uncompressed storage only if output - * would be larger than input. + * 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; |