Fixed memory allocation problems when compressing multi-MB

items. Lookup history is now a double linked list, used in
a wrap-around style.

Jan

diff --git a/src/backend/utils/adt/pg_lzcompress.c b/src/backend/utils/adt/pg_lzcompress.c
index 0c258c0aae30a9453f8148983891b6e4afd0b3ba..9360c60dad777d10e1072c65cb39ad62df6db001 100644 (file)
--- a/src/backend/utils/adt/pg_lzcompress.c
+++ b/src/backend/utils/adt/pg_lzcompress.c
@@ -1,7 +1,7 @@
 /* ----------
  * pg_lzcompress.c -
  *
- * $Header: /cvsroot/pgsql/src/backend/utils/adt/pg_lzcompress.c,v 1.7 2000/07/06 21:02:07 wieck Exp $
+ * $Header: /cvsroot/pgsql/src/backend/utils/adt/pg_lzcompress.c,v 1.8 2000/07/20 14:23:28 wieck Exp $
  *
  *     This is an implementation of LZ compression for PostgreSQL.
  *     It uses a simple history table and generates 2-3 byte tags
@@ -185,9 +185,9 @@
  * Local definitions
  * ----------
  */
-#define PGLZ_HISTORY_SIZE      8192
+#define PGLZ_HISTORY_LISTS     8192
 #define PGLZ_HISTORY_MASK      0x1fff
-#define PGLZ_HISTORY_PREALLOC  8192
+#define PGLZ_HISTORY_SIZE      4096
 #define PGLZ_MAX_MATCH         273
 
 
@@ -200,6 +200,7 @@
 typedef struct PGLZ_HistEntry
 {
    struct PGLZ_HistEntry *next;
+   struct PGLZ_HistEntry *prev;
    char       *pos;
 } PGLZ_HistEntry;
 
@@ -209,7 +210,7 @@ typedef struct PGLZ_HistEntry
  * ----------
  */
 static PGLZ_Strategy strategy_default_data = {
-   256,                        /* Data chunks smaller 256 bytes are nott
+   256,                        /* Data chunks smaller 256 bytes are not
                                 * compressed            */
    6144,                       /* Data chunks greater equal 6K force
                                 * compression               */
@@ -247,6 +248,12 @@ static PGLZ_Strategy strategy_never_data = {
 };
 PGLZ_Strategy *PGLZ_strategy_never = &strategy_never_data;
 
+/* ----------
+ * Global arrays for history
+ * ----------
+ */
+static PGLZ_HistEntry *hist_start[PGLZ_HISTORY_LISTS];
+static PGLZ_HistEntry hist_entries[PGLZ_HISTORY_SIZE];
 
 
 /* ----------
@@ -276,11 +283,26 @@ PGLZ_Strategy *PGLZ_strategy_never = &strategy_never_data;
  *     Adds a new entry to the history table.
  * ----------
  */
-#define pglz_hist_add(_hs,_hn,_s,_e) {                                     \
+#define pglz_hist_add(_hs,_he,_hn,_s,_e) {                                 \
            int __hindex = pglz_hist_idx((_s),(_e));                        \
-           (_hn)->next = (_hs)[__hindex];                                  \
-           (_hn)->pos  = (_s);                                             \
-           (_hs)[__hindex] = (_hn)++;                                      \
+           if ((_he)[(_hn)].prev == NULL) {                                \
+               (_hs)[__hindex] = (_he)[(_hn)].next;                        \
+           } else {                                                        \
+               (_he)[(_hn)].prev->next = (_he)[(_hn)].next;                \
+           }                                                               \
+           if ((_he)[(_hn)].next != NULL) {                                \
+               (_he)[(_hn)].next->prev = (_he)[(_hn)].prev;                \
+           }                                                               \
+           (_he)[(_hn)].next = (_hs)[__hindex];                            \
+           (_he)[(_hn)].prev = NULL;                                       \
+           (_he)[(_hn)].pos  = (_s);                                       \
+           if ((_hs)[__hindex] != NULL) {                                  \
+               (_hs)[__hindex]->prev = &((_he)[(_hn)]);                    \
+           }                                                               \
+           (_hs)[__hindex] = &((_he)[(_hn)]);                              \
+           if (++(_hn) >= PGLZ_HISTORY_SIZE) {                             \
+               (_hn) = 0;                                                  \
+           }                                                               \
        }
 
 
@@ -454,10 +476,7 @@ pglz_find_match(PGLZ_HistEntry **hstart, char *input, char *end,
 int
 pglz_compress(char *source, int slen, PGLZ_Header *dest, PGLZ_Strategy *strategy)
 {
-   PGLZ_HistEntry *hist_start[PGLZ_HISTORY_SIZE];
-   PGLZ_HistEntry *hist_alloc;
-   PGLZ_HistEntry hist_prealloc[PGLZ_HISTORY_PREALLOC];
-   PGLZ_HistEntry *hist_next;
+   int            hist_next = 0;
 
    unsigned char *bp = ((unsigned char *) dest) + sizeof(PGLZ_Header);
    unsigned char *bstart = bp;
@@ -524,17 +543,12 @@ pglz_compress(char *source, int slen, PGLZ_Header *dest, PGLZ_Strategy *strategy
 
    /* ----------
     * Initialize the history tables. For inputs smaller than
-    * PGLZ_HISTORY_PREALLOC, we already have a big enough history
+    * PGLZ_HISTORY_SIZE, we already have a big enough history
     * table on the stack frame.
     * ----------
     */
    memset((void *) hist_start, 0, sizeof(hist_start));
-   if (slen + 1 <= PGLZ_HISTORY_PREALLOC)
-       hist_alloc = hist_prealloc;
-   else
-       hist_alloc = (PGLZ_HistEntry *)
-           palloc(sizeof(PGLZ_HistEntry) * (slen + 1));
-   hist_next = hist_alloc;
+   memset((void *) hist_entries, 0, sizeof(hist_entries));
 
    /* ----------
     * Compute the maximum result size allowed by the strategy.
@@ -588,7 +602,7 @@ pglz_compress(char *source, int slen, PGLZ_Header *dest, PGLZ_Strategy *strategy
            pglz_out_tag(ctrlp, ctrlb, ctrl, bp, match_len, match_off);
            while (match_len--)
            {
-               pglz_hist_add(hist_start, hist_next, dp, dend);
+               pglz_hist_add(hist_start, hist_entries, hist_next, dp, dend);
                dp++;           /* Do not do this ++ in the line above!     */
                /* The macro would do it four times - Jan.  */
            }
@@ -600,19 +614,12 @@ pglz_compress(char *source, int slen, PGLZ_Header *dest, PGLZ_Strategy *strategy
             * ----------
             */
            pglz_out_literal(ctrlp, ctrlb, ctrl, bp, *dp);
-           pglz_hist_add(hist_start, hist_next, dp, dend);
+           pglz_hist_add(hist_start, hist_entries, hist_next, dp, dend);
            dp++;               /* Do not do this ++ in the line above!     */
            /* The macro would do it four times - Jan.  */
        }
    }
 
-   /* ----------
-    * Get rid of the history (if allocated)
-    * ----------
-    */
-   if (hist_alloc != hist_prealloc)
-       pfree((void *) hist_alloc);
-
    /* ----------
     * If we are still in compressing mode, write out the last
     * control byte and determine if the compression gained the