This patch makes the processing of large really large files more efficient
by making sure that the sender's hash table is large enough to hold all the
-checksum entries without being overloaded. It also makes the hashing of
-normal sized files use slightly less memory than before.
+checksum entries without being overloaded. Unfortunately, the code adds a
+modulus calculation for (up to) every byte of the source file, which slows
+down the code for normal file sizes (e.g. 4 CPU seconds slower on a Pentium
+III when copying a 65 MB file without very much matching data).
-An extended version of a patch by Shachar Shemesh.
+This was updated for the latest codebase from a patch written by Shachar
+Shemesh.
+
+To use this patch, run these commands for a successful build:
+
+ patch -p1 <patches/dynamic_hash.diff
+ ./configure (optional if already run)
+ make
--- old/match.c
+++ new/match.c
-@@ -26,11 +26,6 @@ extern int append_mode;
-
- int updating_basis_file;
-
--typedef unsigned short tag;
--
--#define TABLESIZE (1<<16)
--#define NULL_TAG (-1)
--
- static int false_alarms;
- static int tag_hits;
- static int matches;
-@@ -42,47 +37,37 @@ static int total_matches;
+@@ -40,24 +40,31 @@ static int total_matches;
extern struct stats stats;
--struct target {
-- tag t;
-- int32 i;
--};
--
--static struct target *targets;
--
--static int32 *tag_table;
--
--#define gettag2(s1,s2) (((s1) + (s2)) & 0xFFFF)
--#define gettag(sum) gettag2((sum)&0xFFFF,(sum)>>16)
+-#define TABLESIZE (1<<16)
-
--static int compare_targets(struct target *t1,struct target *t2)
--{
-- return (int)t1->t - (int)t2->t;
--}
+static uint32 tablesize;
-+static int32 *sum_table;
+ static int32 *hash_table;
-+#define gettag2(s1,s2) gettag((s1) + ((s2)<<16))
-+#define gettag(sum) ((sum)%tablesize)
+-#define SUM2HASH2(s1,s2) (((s1) + (s2)) & 0xFFFF)
+-#define SUM2HASH(sum) SUM2HASH2((sum)&0xFFFF,(sum)>>16)
++#define SUM2HASH(sum) ((sum)%tablesize)
static void build_hash_table(struct sum_struct *s)
{
int32 i;
+ uint32 prior_size = tablesize;
-- if (!tag_table)
-- tag_table = new_array(int32, TABLESIZE);
+- if (!hash_table) {
+- hash_table = new_array(int32, TABLESIZE);
+ /* Dynamically calculate the hash table size so that the hash load
+ * for big files is about 80%. This number must be odd or s2 will
+ * not be able to span the entire set. */
+ if (tablesize < 65537)
+ tablesize = 65537; /* a prime number */
+ if (tablesize != prior_size) {
-+ free(sum_table);
-+ sum_table = new_array(int32, tablesize);
-+ if (!sum_table)
-+ out_of_memory("build_hash_table");
-+ }
-
-- targets = new_array(struct target, s->count);
-- if (!tag_table || !targets)
-- out_of_memory("build_hash_table");
-+ memset(sum_table, 0xFF, tablesize * sizeof (sum_table[0]));
-
- for (i = 0; i < s->count; i++) {
-- targets[i].i = i;
-- targets[i].t = gettag(s->sums[i].sum1);
-+ uint32 t = gettag(s->sums[i].sum1);
-+ s->sums[i].chain = sum_table[t];
-+ sum_table[t] = i;
- }
--
-- qsort(targets,s->count,sizeof(targets[0]),(int (*)())compare_targets);
--
-- for (i = 0; i < TABLESIZE; i++)
-- tag_table[i] = NULL_TAG;
--
-- for (i = s->count; i-- > 0; )
-- tag_table[targets[i].t] = i;
- }
-
-
-@@ -176,20 +161,17 @@ static void hash_search(int f,struct sum
++ if (hash_table)
++ free(hash_table);
++ hash_table = new_array(int32, tablesize);
+ if (!hash_table)
+ out_of_memory("build_hash_table");
}
- do {
-- tag t = gettag2(s1,s2);
-+ uint32 t = gettag2(s1,s2);
- int done_csum2 = 0;
-- int32 j = tag_table[t];
-+ int32 i;
-
- if (verbose > 4)
- rprintf(FINFO,"offset=%.0f sum=%08x\n",(double)offset,sum);
-
-- if (j == NULL_TAG)
-- goto null_tag;
--
- sum = (s1 & 0xffff) | (s2 << 16);
- tag_hits++;
-- do {
-- int32 l, i = targets[j].i;
-+ for (i = sum_table[t]; i >= 0; i = s->sums[i].chain) {
-+ int32 l;
-
- if (sum != s->sums[i].sum1)
- continue;
-@@ -205,9 +187,10 @@ static void hash_search(int f,struct sum
- && !(s->sums[i].flags & SUMFLG_SAME_OFFSET))
- continue;
+- memset(hash_table, 0xFF, TABLESIZE * sizeof hash_table[0]);
++ memset(hash_table, 0xFF, tablesize * sizeof hash_table[0]);
-- if (verbose > 3)
-- rprintf(FINFO,"potential match at %.0f target=%.0f %.0f sum=%08x\n",
-- (double)offset,(double)j,(double)i,sum);
-+ if (verbose > 3) {
-+ rprintf(FINFO,"potential match at %.0f i=%ld sum=%08x\n",
-+ (double)offset, (long)i, sum);
-+ }
-
- if (!done_csum2) {
- map = (schar *)map_ptr(buf,offset,l);
-@@ -224,23 +207,23 @@ static void hash_search(int f,struct sum
- * one with an identical offset, so we prefer that over
- * the following want_i optimization. */
- if (updating_basis_file) {
-- do {
-- int32 i2 = targets[j].i;
-+ int32 i2;
-+ for (i2 = i; i2 >= 0; i2 = s->sums[i2].chain) {
- if (s->sums[i2].offset != offset)
- continue;
- if (i2 != i) {
- if (sum != s->sums[i2].sum1)
-- break;
-+ continue;
- if (memcmp(sum2, s->sums[i2].sum2,
- s->s2length) != 0)
-- break;
-+ continue;
- i = i2;
- }
- /* This chunk was at the same offset on
- * both the sender and the receiver. */
- s->sums[i].flags |= SUMFLG_SAME_OFFSET;
- goto set_want_i;
-- } while (++j < s->count && targets[j].t == t);
-+ }
- }
-
- /* we've found a match, but now check to see
-@@ -266,9 +249,8 @@ static void hash_search(int f,struct sum
- s2 = sum >> 16;
- matches++;
- break;
-- } while (++j < s->count && targets[j].t == t);
-+ }
-
-- null_tag:
- backup = offset - last_match;
- /* We sometimes read 1 byte prior to last_match... */
- if (backup < 0)
-@@ -375,11 +357,6 @@ void match_sums(int f, struct sum_struct
- rprintf(FINFO,"sending file_sum\n");
- write_buf(f,file_sum,MD4_SUM_LENGTH);
-
-- if (targets) {
-- free(targets);
-- targets=NULL;
-- }
--
- if (verbose > 2)
- rprintf(FINFO, "false_alarms=%d tag_hits=%d matches=%d\n",
- false_alarms, tag_hits, matches);
---- old/rsync.h
-+++ new/rsync.h
-@@ -560,6 +560,7 @@ struct sum_buf {
- OFF_T offset; /**< offset in file of this chunk */
- int32 len; /**< length of chunk of file */
- uint32 sum1; /**< simple checksum */
-+ int32 chain; /**< next hash-table collision */
- short flags; /**< flag bits */
- char sum2[SUM_LENGTH]; /**< checksum */
- };
---- old/sender.c
-+++ new/sender.c
-@@ -92,6 +92,7 @@ static struct sum_struct *receive_sums(i
-
- s->sums[i].offset = offset;
- s->sums[i].flags = 0;
-+ s->sums[i].chain = -1;
-
- if (i == s->count-1 && s->remainder != 0)
- s->sums[i].len = s->remainder;
+ for (i = 0; i < s->count; i++) {
+ uint32 t = SUM2HASH(s->sums[i].sum1);
+@@ -165,11 +172,11 @@ static void hash_search(int f,struct sum
+ (double)offset, s2 & 0xFFFF, s1 & 0xFFFF);
+ }
+
+- i = hash_table[SUM2HASH2(s1,s2)];
++ sum = (s1 & 0xffff) | (s2 << 16);
++ i = hash_table[SUM2HASH(sum)];
+ if (i < 0)
+ goto null_hash;
+
+- sum = (s1 & 0xffff) | (s2 << 16);
+ hash_hits++;
+ do {
+ int32 l;
Matt McCutchen's Web Site / rsync / rsync-patches.git / blobdiff