From 3662afebe8f36b210aaebd6b5e4d599e5620bf15 Mon Sep 17 00:00:00 2001 From: Christoph Berg Date: Thu, 28 Nov 2019 11:46:44 +0100 Subject: [PATCH] Drop our pg_lzcompress copy The local pg_lzcompress copy was never used in the Makefiles, and is only necessary on 9.4 or earlier which is EOL very soon anyway. --- Makefile | 4 +- Makefile.contrib | 2 +- pg_lzcompress.c | 778 ----------------------------------------------- 3 files changed, 3 insertions(+), 781 deletions(-) delete mode 100644 pg_lzcompress.c diff --git a/Makefile b/Makefile index 98ca550..8c32cc7 100644 --- a/Makefile +++ b/Makefile @@ -4,7 +4,7 @@ FD_VERSION=11.0 PROGRAM = pg_filedump -OBJS = pg_filedump.o decode.o stringinfo.o pg_lzcompress.o +OBJS = pg_filedump.o decode.o stringinfo.o PG_CONFIG = pg_config PGXS := $(shell $(PG_CONFIG) --pgxs) @@ -14,7 +14,7 @@ include $(PGXS) LIBS = $(libpq_pgport) DISTFILES= README.pg_filedump Makefile Makefile.contrib \ - pg_filedump.h pg_filedump.c decode.h decode.c stringinfo.c pg_lzcompress.c + pg_filedump.h pg_filedump.c decode.h decode.c stringinfo.c dist: rm -rf pg_filedump-${FD_VERSION} pg_filedump-${FD_VERSION}.tar.gz diff --git a/Makefile.contrib b/Makefile.contrib index 9668b93..b9a89aa 100644 --- a/Makefile.contrib +++ b/Makefile.contrib @@ -1,5 +1,5 @@ PROGRAM = pg_filedump -OBJS = decode.o pg_filedump.o pg_lzcompress.o stringinfo.o +OBJS = decode.o pg_filedump.o stringinfo.o DOCS = README.pg_filedump diff --git a/pg_lzcompress.c b/pg_lzcompress.c deleted file mode 100644 index a2f87cf..0000000 --- a/pg_lzcompress.c +++ /dev/null @@ -1,778 +0,0 @@ -/* ---------- - * pg_lzcompress.c - - * - * This is an implementation of LZ compression for PostgreSQL. - * It uses a simple history table and generates 2-3 byte tags - * capable of backward copy information for 3-273 bytes with - * a max offset of 4095. - * - * Entry routines: - * - * int32 - * pglz_compress(const char *source, int32 slen, char *dest, - * const PGLZ_Strategy *strategy); - * - * source is the input data to be compressed. - * - * slen is the length of the input data. - * - * dest is the output area for the compressed result. - * It must be at least as big as PGLZ_MAX_OUTPUT(slen). - * - * strategy is a pointer to some information controlling - * the compression algorithm. If NULL, the compiled - * in default strategy is used. - * - * The return value is the number of bytes written in the - * buffer dest, or -1 if compression fails; in the latter - * case the contents of dest are undefined. - * - * int32 - * pglz_decompress(const char *source, int32 slen, char *dest, - * int32 rawsize) - * - * source is the compressed input. - * - * slen is the length of the compressed input. - * - * dest is the area where the uncompressed data will be - * written to. It is the callers responsibility to - * provide enough space. - * - * The data is written to buff exactly as it was handed - * to pglz_compress(). No terminating zero byte is added. - * - * rawsize is the length of the uncompressed data. - * - * The return value is the number of bytes written in the - * buffer dest, or -1 if decompression fails. - * - * The decompression algorithm and internal data format: - * - * It is made with the compressed data itself. - * - * The data representation is easiest explained by describing - * the process of decompression. - * - * If compressed_size == rawsize, then the data - * is stored uncompressed as plain bytes. Thus, the decompressor - * simply copies rawsize bytes to the destination. - * - * Otherwise the first byte tells what to do the next 8 times. - * We call this the control byte. - * - * An unset bit in the control byte means, that one uncompressed - * byte follows, which is copied from input to output. - * - * A set bit in the control byte means, that a tag of 2-3 bytes - * follows. A tag contains information to copy some bytes, that - * are already in the output buffer, to the current location in - * the output. Let's call the three tag bytes T1, T2 and T3. The - * position of the data to copy is coded as an offset from the - * actual output position. - * - * The offset is in the upper nibble of T1 and in T2. - * The length is in the lower nibble of T1. - * - * So the 16 bits of a 2 byte tag are coded as - * - * 7---T1--0 7---T2--0 - * OOOO LLLL OOOO OOOO - * - * This limits the offset to 1-4095 (12 bits) and the length - * to 3-18 (4 bits) because 3 is always added to it. To emit - * a tag of 2 bytes with a length of 2 only saves one control - * bit. But we lose one byte in the possible length of a tag. - * - * In the actual implementation, the 2 byte tag's length is - * limited to 3-17, because the value 0xF in the length nibble - * has special meaning. It means, that the next following - * byte (T3) has to be added to the length value of 18. That - * makes total limits of 1-4095 for offset and 3-273 for length. - * - * Now that we have successfully decoded a tag. We simply copy - * the output that occurred bytes back to the current - * output location in the specified . Thus, a - * sequence of 200 spaces (think about bpchar fields) could be - * coded in 4 bytes. One literal space and a three byte tag to - * copy 199 bytes with a -1 offset. Whow - that's a compression - * rate of 98%! Well, the implementation needs to save the - * original data size too, so we need another 4 bytes for it - * and end up with a total compression rate of 96%, what's still - * worth a Whow. - * - * The compression algorithm - * - * The following uses numbers used in the default strategy. - * - * The compressor works best for attributes of a size between - * 1K and 1M. For smaller items there's not that much chance of - * redundancy in the character sequence (except for large areas - * of identical bytes like trailing spaces) and for bigger ones - * our 4K maximum look-back distance is too small. - * - * The compressor creates a table for lists of positions. - * For each input position (except the last 3), a hash key is - * built from the 4 next input bytes and the position remembered - * in the appropriate list. Thus, the table points to linked - * lists of likely to be at least in the first 4 characters - * matching strings. This is done on the fly while the input - * is compressed into the output area. Table entries are only - * kept for the last 4096 input positions, since we cannot use - * back-pointers larger than that anyway. The size of the hash - * table is chosen based on the size of the input - a larger table - * has a larger startup cost, as it needs to be initialized to - * zero, but reduces the number of hash collisions on long inputs. - * - * For each byte in the input, its hash key (built from this - * byte and the next 3) is used to find the appropriate list - * in the table. The lists remember the positions of all bytes - * that had the same hash key in the past in increasing backward - * offset order. Now for all entries in the used lists, the - * match length is computed by comparing the characters from the - * entries position with the characters from the actual input - * position. - * - * The compressor starts with a so called "good_match" of 128. - * It is a "prefer speed against compression ratio" optimizer. - * So if the first entry looked at already has 128 or more - * matching characters, the lookup stops and that position is - * used for the next tag in the output. - * - * For each subsequent entry in the history list, the "good_match" - * is lowered by 10%. So the compressor will be more happy with - * short matches the farer it has to go back in the history. - * Another "speed against ratio" preference characteristic of - * the algorithm. - * - * Thus there are 3 stop conditions for the lookup of matches: - * - * - a match >= good_match is found - * - there are no more history entries to look at - * - the next history entry is already too far back - * to be coded into a tag. - * - * Finally the match algorithm checks that at least a match - * of 3 or more bytes has been found, because that is the smallest - * amount of copy information to code into a tag. If so, a tag - * is omitted and all the input bytes covered by that are just - * scanned for the history add's, otherwise a literal character - * is omitted and only his history entry added. - * - * Acknowledgements: - * - * Many thanks to Adisak Pochanayon, who's article about SLZ - * inspired me to write the PostgreSQL compression this way. - * - * Jan Wieck - * - * Copyright (c) 1999-2018, PostgreSQL Global Development Group - * - * src/common/pg_lzcompress.c - * ---------- - */ -#ifndef FRONTEND -#include "postgres.h" -#else -#include "postgres_fe.h" -#endif - -#include - -#include "common/pg_lzcompress.h" - - -/* ---------- - * Local definitions - * ---------- - */ -#define PGLZ_MAX_HISTORY_LISTS 8192 /* must be power of 2 */ -#define PGLZ_HISTORY_SIZE 4096 -#define PGLZ_MAX_MATCH 273 - - -/* ---------- - * PGLZ_HistEntry - - * - * Linked list for the backward history lookup - * - * All the entries sharing a hash key are linked in a doubly linked list. - * This makes it easy to remove an entry when it's time to recycle it - * (because it's more than 4K positions old). - * ---------- - */ -typedef struct PGLZ_HistEntry -{ - struct PGLZ_HistEntry *next; /* links for my hash key's list */ - struct PGLZ_HistEntry *prev; - int hindex; /* my current hash key */ - const char *pos; /* my input position */ -} PGLZ_HistEntry; - - -/* ---------- - * The provided standard strategies - * ---------- - */ -static const PGLZ_Strategy strategy_default_data = { - 32, /* Data chunks less than 32 bytes are not - * compressed */ - INT_MAX, /* No upper limit on what we'll try to - * compress */ - 25, /* Require 25% compression rate, or not worth - * it */ - 1024, /* Give up if no compression in the first 1KB */ - 128, /* Stop history lookup if a match of 128 bytes - * is found */ - 10 /* Lower good match size by 10% at every loop - * iteration */ -}; -const PGLZ_Strategy *const PGLZ_strategy_default = &strategy_default_data; - - -static const PGLZ_Strategy strategy_always_data = { - 0, /* Chunks of any size are compressed */ - INT_MAX, - 0, /* It's enough to save one single byte */ - INT_MAX, /* Never give up early */ - 128, /* Stop history lookup if a match of 128 bytes - * is found */ - 6 /* Look harder for a good match */ -}; -const PGLZ_Strategy *const PGLZ_strategy_always = &strategy_always_data; - - -/* ---------- - * Statically allocated work arrays for history - * ---------- - */ -static int16 hist_start[PGLZ_MAX_HISTORY_LISTS]; -static PGLZ_HistEntry hist_entries[PGLZ_HISTORY_SIZE + 1]; - -/* - * Element 0 in hist_entries is unused, and means 'invalid'. Likewise, - * INVALID_ENTRY_PTR in next/prev pointers mean 'invalid'. - */ -#define INVALID_ENTRY 0 -#define INVALID_ENTRY_PTR (&hist_entries[INVALID_ENTRY]) - -/* ---------- - * pglz_hist_idx - - * - * Computes the history table slot for the lookup by the next 4 - * characters in the input. - * - * NB: because we use the next 4 characters, we are not guaranteed to - * find 3-character matches; they very possibly will be in the wrong - * hash list. This seems an acceptable tradeoff for spreading out the - * hash keys more. - * ---------- - */ -#define pglz_hist_idx(_s,_e, _mask) ( \ - ((((_e) - (_s)) < 4) ? (int) (_s)[0] : \ - (((_s)[0] << 6) ^ ((_s)[1] << 4) ^ \ - ((_s)[2] << 2) ^ (_s)[3])) & (_mask) \ - ) - - -/* ---------- - * pglz_hist_add - - * - * Adds a new entry to the history table. - * - * If _recycle is true, then we are recycling a previously used entry, - * and must first delink it from its old hashcode's linked list. - * - * NOTE: beware of multiple evaluations of macro's arguments, and note that - * _hn and _recycle are modified in the macro. - * ---------- - */ -#define pglz_hist_add(_hs,_he,_hn,_recycle,_s,_e, _mask) \ -do { \ - int __hindex = pglz_hist_idx((_s),(_e), (_mask)); \ - int16 *__myhsp = &(_hs)[__hindex]; \ - PGLZ_HistEntry *__myhe = &(_he)[_hn]; \ - if (_recycle) { \ - if (__myhe->prev == NULL) \ - (_hs)[__myhe->hindex] = __myhe->next - (_he); \ - else \ - __myhe->prev->next = __myhe->next; \ - if (__myhe->next != NULL) \ - __myhe->next->prev = __myhe->prev; \ - } \ - __myhe->next = &(_he)[*__myhsp]; \ - __myhe->prev = NULL; \ - __myhe->hindex = __hindex; \ - __myhe->pos = (_s); \ - /* If there was an existing entry in this hash slot, link */ \ - /* this new entry to it. However, the 0th entry in the */ \ - /* entries table is unused, so we can freely scribble on it. */ \ - /* So don't bother checking if the slot was used - we'll */ \ - /* scribble on the unused entry if it was not, but that's */ \ - /* harmless. Avoiding the branch in this critical path */ \ - /* speeds this up a little bit. */ \ - /* if (*__myhsp != INVALID_ENTRY) */ \ - (_he)[(*__myhsp)].prev = __myhe; \ - *__myhsp = _hn; \ - if (++(_hn) >= PGLZ_HISTORY_SIZE + 1) { \ - (_hn) = 1; \ - (_recycle) = true; \ - } \ -} while (0) - - -/* ---------- - * pglz_out_ctrl - - * - * Outputs the last and allocates a new control byte if needed. - * ---------- - */ -#define pglz_out_ctrl(__ctrlp,__ctrlb,__ctrl,__buf) \ -do { \ - if ((__ctrl & 0xff) == 0) \ - { \ - *(__ctrlp) = __ctrlb; \ - __ctrlp = (__buf)++; \ - __ctrlb = 0; \ - __ctrl = 1; \ - } \ -} while (0) - - -/* ---------- - * pglz_out_literal - - * - * Outputs a literal byte to the destination buffer including the - * appropriate control bit. - * ---------- - */ -#define pglz_out_literal(_ctrlp,_ctrlb,_ctrl,_buf,_byte) \ -do { \ - pglz_out_ctrl(_ctrlp,_ctrlb,_ctrl,_buf); \ - *(_buf)++ = (unsigned char)(_byte); \ - _ctrl <<= 1; \ -} while (0) - - -/* ---------- - * pglz_out_tag - - * - * Outputs a backward reference tag of 2-4 bytes (depending on - * offset and length) to the destination buffer including the - * appropriate control bit. - * ---------- - */ -#define pglz_out_tag(_ctrlp,_ctrlb,_ctrl,_buf,_len,_off) \ -do { \ - pglz_out_ctrl(_ctrlp,_ctrlb,_ctrl,_buf); \ - _ctrlb |= _ctrl; \ - _ctrl <<= 1; \ - if (_len > 17) \ - { \ - (_buf)[0] = (unsigned char)((((_off) & 0xf00) >> 4) | 0x0f); \ - (_buf)[1] = (unsigned char)(((_off) & 0xff)); \ - (_buf)[2] = (unsigned char)((_len) - 18); \ - (_buf) += 3; \ - } else { \ - (_buf)[0] = (unsigned char)((((_off) & 0xf00) >> 4) | ((_len) - 3)); \ - (_buf)[1] = (unsigned char)((_off) & 0xff); \ - (_buf) += 2; \ - } \ -} while (0) - - -/* ---------- - * pglz_find_match - - * - * Lookup the history table if the actual input stream matches - * another sequence of characters, starting somewhere earlier - * in the input buffer. - * ---------- - */ -static inline int -pglz_find_match(int16 *hstart, const char *input, const char *end, - int *lenp, int *offp, int good_match, int good_drop, int mask) -{ - PGLZ_HistEntry *hent; - int16 hentno; - int32 len = 0; - int32 off = 0; - - /* - * Traverse the linked history list until a good enough match is found. - */ - hentno = hstart[pglz_hist_idx(input, end, mask)]; - hent = &hist_entries[hentno]; - while (hent != INVALID_ENTRY_PTR) - { - const char *ip = input; - const char *hp = hent->pos; - int32 thisoff; - int32 thislen; - - /* - * Stop if the offset does not fit into our tag anymore. - */ - thisoff = ip - hp; - if (thisoff >= 0x0fff) - break; - - /* - * Determine length of match. A better match must be larger than the - * best so far. And if we already have a match of 16 or more bytes, - * it's worth the call overhead to use memcmp() to check if this match - * is equal for the same size. After that we must fallback to - * character by character comparison to know the exact position where - * the diff occurred. - */ - thislen = 0; - if (len >= 16) - { - if (memcmp(ip, hp, len) == 0) - { - thislen = len; - ip += len; - hp += len; - while (ip < end && *ip == *hp && thislen < PGLZ_MAX_MATCH) - { - thislen++; - ip++; - hp++; - } - } - } - else - { - while (ip < end && *ip == *hp && thislen < PGLZ_MAX_MATCH) - { - thislen++; - ip++; - hp++; - } - } - - /* - * Remember this match as the best (if it is) - */ - if (thislen > len) - { - len = thislen; - off = thisoff; - } - - /* - * Advance to the next history entry - */ - hent = hent->next; - - /* - * Be happy with lesser good matches the more entries we visited. But - * no point in doing calculation if we're at end of list. - */ - if (hent != INVALID_ENTRY_PTR) - { - if (len >= good_match) - break; - good_match -= (good_match * good_drop) / 100; - } - } - - /* - * Return match information only if it results at least in one byte - * reduction. - */ - if (len > 2) - { - *lenp = len; - *offp = off; - return 1; - } - - return 0; -} - - -/* ---------- - * pglz_compress - - * - * Compresses source into dest using strategy. Returns the number of - * bytes written in buffer dest, or -1 if compression fails. - * ---------- - */ -int32 -pglz_compress(const char *source, int32 slen, char *dest, - const PGLZ_Strategy *strategy) -{ - unsigned char *bp = (unsigned char *) dest; - unsigned char *bstart = bp; - int hist_next = 1; - bool hist_recycle = false; - const char *dp = source; - const char *dend = source + slen; - unsigned char ctrl_dummy = 0; - unsigned char *ctrlp = &ctrl_dummy; - unsigned char ctrlb = 0; - unsigned char ctrl = 0; - bool found_match = false; - int32 match_len; - int32 match_off; - int32 good_match; - int32 good_drop; - int32 result_size; - int32 result_max; - int32 need_rate; - int hashsz; - int mask; - - /* - * Our fallback strategy is the default. - */ - if (strategy == NULL) - strategy = PGLZ_strategy_default; - - /* - * If the strategy forbids compression (at all or if source chunk size out - * of range), fail. - */ - if (strategy->match_size_good <= 0 || - slen < strategy->min_input_size || - slen > strategy->max_input_size) - return -1; - - /* - * Limit the match parameters to the supported range. - */ - good_match = strategy->match_size_good; - if (good_match > PGLZ_MAX_MATCH) - good_match = PGLZ_MAX_MATCH; - else if (good_match < 17) - good_match = 17; - - good_drop = strategy->match_size_drop; - if (good_drop < 0) - good_drop = 0; - else if (good_drop > 100) - good_drop = 100; - - need_rate = strategy->min_comp_rate; - if (need_rate < 0) - need_rate = 0; - else if (need_rate > 99) - need_rate = 99; - - /* - * Compute the maximum result size allowed by the strategy, namely the - * input size minus the minimum wanted compression rate. This had better - * be <= slen, else we might overrun the provided output buffer. - */ - if (slen > (INT_MAX / 100)) - { - /* Approximate to avoid overflow */ - result_max = (slen / 100) * (100 - need_rate); - } - else - result_max = (slen * (100 - need_rate)) / 100; - - /* - * Experiments suggest that these hash sizes work pretty well. A large - * hash table minimizes collision, but has a higher startup cost. For a - * small input, the startup cost dominates. The table size must be a power - * of two. - */ - if (slen < 128) - hashsz = 512; - else if (slen < 256) - hashsz = 1024; - else if (slen < 512) - hashsz = 2048; - else if (slen < 1024) - hashsz = 4096; - else - hashsz = 8192; - mask = hashsz - 1; - - /* - * Initialize the history lists to empty. We do not need to zero the - * hist_entries[] array; its entries are initialized as they are used. - */ - memset(hist_start, 0, hashsz * sizeof(int16)); - - /* - * Compress the source directly into the output buffer. - */ - while (dp < dend) - { - /* - * If we already exceeded the maximum result size, fail. - * - * We check once per loop; since the loop body could emit as many as 4 - * bytes (a control byte and 3-byte tag), PGLZ_MAX_OUTPUT() had better - * allow 4 slop bytes. - */ - if (bp - bstart >= result_max) - return -1; - - /* - * If we've emitted more than first_success_by bytes without finding - * anything compressible at all, fail. This lets us fall out - * reasonably quickly when looking at incompressible input (such as - * pre-compressed data). - */ - if (!found_match && bp - bstart >= strategy->first_success_by) - return -1; - - /* - * Try to find a match in the history - */ - if (pglz_find_match(hist_start, dp, dend, &match_len, - &match_off, good_match, good_drop, mask)) - { - /* - * Create the tag and add history entries for all matched - * characters. - */ - pglz_out_tag(ctrlp, ctrlb, ctrl, bp, match_len, match_off); - while (match_len--) - { - pglz_hist_add(hist_start, hist_entries, - hist_next, hist_recycle, - dp, dend, mask); - dp++; /* Do not do this ++ in the line above! */ - /* The macro would do it four times - Jan. */ - } - found_match = true; - } - else - { - /* - * No match found. Copy one literal byte. - */ - pglz_out_literal(ctrlp, ctrlb, ctrl, bp, *dp); - pglz_hist_add(hist_start, hist_entries, - hist_next, hist_recycle, - dp, dend, mask); - dp++; /* Do not do this ++ in the line above! */ - /* The macro would do it four times - Jan. */ - } - } - - /* - * Write out the last control byte and check that we haven't overrun the - * output size allowed by the strategy. - */ - *ctrlp = ctrlb; - result_size = bp - bstart; - if (result_size >= result_max) - return -1; - - /* success */ - return result_size; -} - - -/* ---------- - * pglz_decompress - - * - * Decompresses source into dest. Returns the number of bytes - * decompressed in the destination buffer, or -1 if decompression - * fails. - * ---------- - */ -int32 -pglz_decompress(const char *source, int32 slen, char *dest, - int32 rawsize) -{ - const unsigned char *sp; - const unsigned char *srcend; - unsigned char *dp; - unsigned char *destend; - - sp = (const unsigned char *) source; - srcend = ((const unsigned char *) source) + slen; - dp = (unsigned char *) dest; - destend = dp + rawsize; - - while (sp < srcend && dp < destend) - { - /* - * Read one control byte and process the next 8 items (or as many as - * remain in the compressed input). - */ - unsigned char ctrl = *sp++; - int ctrlc; - - for (ctrlc = 0; ctrlc < 8 && sp < srcend; ctrlc++) - { - if (ctrl & 1) - { - /* - * Otherwise it contains the match length minus 3 and the - * upper 4 bits of the offset. The next following byte - * contains the lower 8 bits of the offset. If the length is - * coded as 18, another extension tag byte tells how much - * longer the match really was (0-255). - */ - int32 len; - int32 off; - - len = (sp[0] & 0x0f) + 3; - off = ((sp[0] & 0xf0) << 4) | sp[1]; - sp += 2; - if (len == 18) - len += *sp++; - - /* - * Check for output buffer overrun, to ensure we don't clobber - * memory in case of corrupt input. Note: we must advance dp - * here to ensure the error is detected below the loop. We - * don't simply put the elog inside the loop since that will - * probably interfere with optimization. - */ - if (dp + len > destend) - { - dp += len; - break; - } - - /* - * Now we copy the bytes specified by the tag from OUTPUT to - * OUTPUT. It is dangerous and platform dependent to use - * memcpy() here, because the copied areas could overlap - * extremely! - */ - while (len--) - { - *dp = dp[-off]; - dp++; - } - } - else - { - /* - * An unset control bit means LITERAL BYTE. So we just copy - * one from INPUT to OUTPUT. - */ - if (dp >= destend) /* check for buffer overrun */ - break; /* do not clobber memory */ - - *dp++ = *sp++; - } - - /* - * Advance the control bit - */ - ctrl >>= 1; - } - } - - /* - * Check we decompressed the right amount. - */ - if (dp != destend || sp != srcend) - return -1; - - /* - * That's it. - */ - return rawsize; -} -- 2.39.5