Merge pull request #6903 from oranagra/defrag_lists

Defrag big lists in portions to avoid latency and freeze

src/defrag.c

@@ -5,8 +5,8 @@
  * We do that by scanning the keyspace and for each pointer we have, we can try to
  * ask the allocator if moving it to a new address will help reduce fragmentation.
  *
- * Copyright (c) 2017, Oran Agra
+ * Copyright (c) 2020, Oran Agra
- * Copyright (c) 2017, Redis Labs, Inc
+ * Copyright (c) 2020, Redis Labs, Inc
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -408,25 +408,32 @@ dictEntry* replaceSateliteDictKeyPtrAndOrDefragDictEntry(dict *d, sds oldkey, sd
     return NULL;
 }
 
-long activeDefragQuickListNodes(quicklist *ql) {
+long activeDefragQuickListNode(quicklist *ql, quicklistNode **node_ref) {
-    quicklistNode *node = ql->head, *newnode;
+    quicklistNode *newnode, *node = *node_ref;
     long defragged = 0;
     unsigned char *newzl;
+    if ((newnode = activeDefragAlloc(node))) {
+        if (newnode->prev)
+            newnode->prev->next = newnode;
+        else
+            ql->head = newnode;
+        if (newnode->next)
+            newnode->next->prev = newnode;
+        else
+            ql->tail = newnode;
+        *node_ref = node = newnode;
+        defragged++;
+    }
+    if ((newzl = activeDefragAlloc(node->zl)))
+        defragged++, node->zl = newzl;
+    return defragged;
+}
+
+long activeDefragQuickListNodes(quicklist *ql) {
+    quicklistNode *node = ql->head;
+    long defragged = 0;
     while (node) {
-        if ((newnode = activeDefragAlloc(node))) {
+        defragged += activeDefragQuickListNode(ql, &node);
-            if (newnode->prev)
-                newnode->prev->next = newnode;
-            else
-                ql->head = newnode;
-            if (newnode->next)
-                newnode->next->prev = newnode;
-            else
-                ql->tail = newnode;
-            node = newnode;
-            defragged++;
-        }
-        if ((newzl = activeDefragAlloc(node->zl)))
-            defragged++, node->zl = newzl;
         node = node->next;
     }
     return defragged;
@@ -440,12 +447,48 @@ void defragLater(redisDb *db, dictEntry *kde) {
     listAddNodeTail(db->defrag_later, key);
 }
 
-long scanLaterList(robj *ob) {
+/* returns 0 if no more work needs to be been done, and 1 if time is up and more work is needed. */
+long scanLaterList(robj *ob, unsigned long *cursor, long long endtime, long long *defragged) {
     quicklist *ql = ob->ptr;
+    quicklistNode *node;
+    long iterations = 0;
+    int bookmark_failed = 0;
     if (ob->type != OBJ_LIST || ob->encoding != OBJ_ENCODING_QUICKLIST)
         return 0;
-    server.stat_active_defrag_scanned+=ql->len;
+
-    return activeDefragQuickListNodes(ql);
+    if (*cursor == 0) {
+        /* if cursor is 0, we start new iteration */
+        node = ql->head;
+    } else {
+        node = quicklistBookmarkFind(ql, "_AD");
+        if (!node) {
+            /* if the bookmark was deleted, it means we reached the end. */
+            *cursor = 0;
+            return 0;
+        }
+        node = node->next;
+    }
+
+    (*cursor)++;
+    while (node) {
+        (*defragged) += activeDefragQuickListNode(ql, &node);
+        server.stat_active_defrag_scanned++;
+        if (++iterations > 128 && !bookmark_failed) {
+            if (ustime() > endtime) {
+                if (!quicklistBookmarkCreate(&ql, "_AD", node)) {
+                    bookmark_failed = 1;
+                } else {
+                    ob->ptr = ql; /* bookmark creation may have re-allocated the quicklist */
+                    return 1;
+                }
+            }
+            iterations = 0;
+        }
+        node = node->next;
+    }
+    quicklistBookmarkDelete(ql, "_AD");
+    *cursor = 0;
+    return bookmark_failed? 1: 0;
 }
 
 typedef struct {
@@ -638,7 +681,8 @@ int scanLaterStraemListpacks(robj *ob, unsigned long *cursor, long long endtime,
         void *newdata = activeDefragAlloc(ri.data);
         if (newdata)
             raxSetData(ri.node, ri.data=newdata), (*defragged)++;
-        if (++iterations > 16) {
+        server.stat_active_defrag_scanned++;
+        if (++iterations > 128) {
             if (ustime() > endtime) {
                 serverAssert(ri.key_len==sizeof(last));
                 memcpy(last,ri.key,ri.key_len);
@@ -900,8 +944,7 @@ int defragLaterItem(dictEntry *de, unsigned long *cursor, long long endtime) {
     if (de) {
         robj *ob = dictGetVal(de);
         if (ob->type == OBJ_LIST) {
-            server.stat_active_defrag_hits += scanLaterList(ob);
+            return scanLaterList(ob, cursor, endtime, &server.stat_active_defrag_hits);
-            *cursor = 0; /* list has no scan, we must finish it in one go */
         } else if (ob->type == OBJ_SET) {
             server.stat_active_defrag_hits += scanLaterSet(ob, cursor);
         } else if (ob->type == OBJ_ZSET) {
@@ -961,11 +1004,6 @@ int defragLaterStep(redisDb *db, long long endtime) {
             if (defragLaterItem(de, &defrag_later_cursor, endtime))
                 quit = 1; /* time is up, we didn't finish all the work */
 
-            /* Don't start a new BIG key in this loop, this is because the
-             * next key can be a list, and scanLaterList must be done in once cycle */
-            if (!defrag_later_cursor)
-                quit = 1;
-
             /* Once in 16 scan iterations, 512 pointer reallocations, or 64 fields
              * (if we have a lot of pointers in one hash bucket, or rehashing),
              * check if we reached the time limit. */

src/quicklist.c

@@ -70,6 +70,12 @@ static const size_t optimization_level[] = {4096, 8192, 16384, 32768, 65536};
     } while (0);
 #endif
 
+/* Bookmarks forward declarations */
+#define QL_MAX_BM ((1 << QL_BM_BITS)-1)
+quicklistBookmark *_quicklistBookmarkFindByName(quicklist *ql, const char *name);
+quicklistBookmark *_quicklistBookmarkFindByNode(quicklist *ql, quicklistNode *node);
+void _quicklistBookmarkDelete(quicklist *ql, quicklistBookmark *bm);
+
 /* Simple way to give quicklistEntry structs default values with one call. */
 #define initEntry(e)                                                           \
     do {                                                                       \
@@ -100,10 +106,11 @@ quicklist *quicklistCreate(void) {
     quicklist->count = 0;
     quicklist->compress = 0;
     quicklist->fill = -2;
+    quicklist->bookmark_count = 0;
     return quicklist;
 }
 
-#define COMPRESS_MAX (1 << 16)
+#define COMPRESS_MAX (1 << QL_COMP_BITS)
 void quicklistSetCompressDepth(quicklist *quicklist, int compress) {
     if (compress > COMPRESS_MAX) {
         compress = COMPRESS_MAX;
@@ -113,7 +120,7 @@ void quicklistSetCompressDepth(quicklist *quicklist, int compress) {
     quicklist->compress = compress;
 }
 
-#define FILL_MAX (1 << 15)
+#define FILL_MAX (1 << (QL_FILL_BITS-1))
 void quicklistSetFill(quicklist *quicklist, int fill) {
     if (fill > FILL_MAX) {
         fill = FILL_MAX;
@@ -169,6 +176,7 @@ void quicklistRelease(quicklist *quicklist) {
         quicklist->len--;
         current = next;
     }
+    quicklistBookmarksClear(quicklist);
     zfree(quicklist);
 }
 
@@ -578,6 +586,15 @@ quicklist *quicklistCreateFromZiplist(int fill, int compress,
 
 REDIS_STATIC void __quicklistDelNode(quicklist *quicklist,
                                      quicklistNode *node) {
+    /* Update the bookmark if any */
+    quicklistBookmark *bm = _quicklistBookmarkFindByNode(quicklist, node);
+    if (bm) {
+        bm->node = node->next;
+        /* if the bookmark was to the last node, delete it. */
+        if (!bm->node)
+            _quicklistBookmarkDelete(quicklist, bm);
+    }
+
     if (node->next)
         node->next->prev = node->prev;
     if (node->prev)
@@ -1410,6 +1427,87 @@ void quicklistPush(quicklist *quicklist, void *value, const size_t sz,
     }
 }
 
+/* Create or update a bookmark in the list which will be updated to the next node
+ * automatically when the one referenced gets deleted.
+ * Returns 1 on success (creation of new bookmark or override of an existing one).
+ * Returns 0 on failure (reached the maximum supported number of bookmarks).
+ * NOTE: use short simple names, so that string compare on find is quick.
+ * NOTE: bookmakrk creation may re-allocate the quicklist, so the input pointer
+         may change and it's the caller responsibilty to update the reference.
+ */
+int quicklistBookmarkCreate(quicklist **ql_ref, const char *name, quicklistNode *node) {
+    quicklist *ql = *ql_ref;
+    if (ql->bookmark_count >= QL_MAX_BM)
+        return 0;
+    quicklistBookmark *bm = _quicklistBookmarkFindByName(ql, name);
+    if (bm) {
+        bm->node = node;
+        return 1;
+    }
+    ql = zrealloc(ql, sizeof(quicklist) + (ql->bookmark_count+1) * sizeof(quicklistBookmark));
+    *ql_ref = ql;
+    ql->bookmarks[ql->bookmark_count].node = node;
+    ql->bookmarks[ql->bookmark_count].name = zstrdup(name);
+    ql->bookmark_count++;
+    return 1;
+}
+
+/* Find the quicklist node referenced by a named bookmark.
+ * When the bookmarked node is deleted the bookmark is updated to the next node,
+ * and if that's the last node, the bookmark is deleted (so find returns NULL). */
+quicklistNode *quicklistBookmarkFind(quicklist *ql, const char *name) {
+    quicklistBookmark *bm = _quicklistBookmarkFindByName(ql, name);
+    if (!bm) return NULL;
+    return bm->node;
+}
+
+/* Delete a named bookmark.
+ * returns 0 if bookmark was not found, and 1 if deleted.
+ * Note that the bookmark memory is not freed yet, and is kept for future use. */
+int quicklistBookmarkDelete(quicklist *ql, const char *name) {
+    quicklistBookmark *bm = _quicklistBookmarkFindByName(ql, name);
+    if (!bm)
+        return 0;
+    _quicklistBookmarkDelete(ql, bm);
+    return 1;
+}
+
+quicklistBookmark *_quicklistBookmarkFindByName(quicklist *ql, const char *name) {
+    unsigned i;
+    for (i=0; i<ql->bookmark_count; i++) {
+        if (!strcmp(ql->bookmarks[i].name, name)) {
+            return &ql->bookmarks[i];
+        }
+    }
+    return NULL;
+}
+
+quicklistBookmark *_quicklistBookmarkFindByNode(quicklist *ql, quicklistNode *node) {
+    unsigned i;
+    for (i=0; i<ql->bookmark_count; i++) {
+        if (ql->bookmarks[i].node == node) {
+            return &ql->bookmarks[i];
+        }
+    }
+    return NULL;
+}
+
+void _quicklistBookmarkDelete(quicklist *ql, quicklistBookmark *bm) {
+    int index = bm - ql->bookmarks;
+    zfree(bm->name);
+    ql->bookmark_count--;
+    memmove(bm, bm+1, (ql->bookmark_count - index)* sizeof(*bm));
+    /* NOTE: We do not shrink (realloc) the quicklist yet (to avoid resonance,
+     * it may be re-used later (a call to realloc may NOP). */
+}
+
+void quicklistBookmarksClear(quicklist *ql) {
+    while (ql->bookmark_count)
+        zfree(ql->bookmarks[--ql->bookmark_count].name);
+    /* NOTE: We do not shrink (realloc) the quick list. main use case for this
+     * function is just before releasing the allocation. */
+}
+
 /* The rest of this file is test cases and test helpers. */
 #ifdef REDIS_TEST
 #include <stdint.h>
@@ -2641,6 +2739,54 @@ int quicklistTest(int argc, char *argv[]) {
     printf("Compressions: %0.2f seconds.\n", (float)(stop - start) / 1000);
     printf("\n");
 
+    TEST("bookmark get updated to next item") {
+        quicklist *ql = quicklistNew(1, 0);
+        quicklistPushTail(ql, "1", 1);
+        quicklistPushTail(ql, "2", 1);
+        quicklistPushTail(ql, "3", 1);
+        quicklistPushTail(ql, "4", 1);
+        quicklistPushTail(ql, "5", 1);
+        assert(ql->len==5);
+        /* add two bookmarks, one pointing to the node before the last. */
+        assert(quicklistBookmarkCreate(&ql, "_dummy", ql->head->next));
+        assert(quicklistBookmarkCreate(&ql, "_test", ql->tail->prev));
+        /* test that the bookmark returns the right node, delete it and see that the bookmark points to the last node */
+        assert(quicklistBookmarkFind(ql, "_test") == ql->tail->prev);
+        assert(quicklistDelRange(ql, -2, 1));
+        assert(quicklistBookmarkFind(ql, "_test") == ql->tail);
+        /* delete the last node, and see that the bookmark was deleted. */
+        assert(quicklistDelRange(ql, -1, 1));
+        assert(quicklistBookmarkFind(ql, "_test") == NULL);
+        /* test that other bookmarks aren't affected */
+        assert(quicklistBookmarkFind(ql, "_dummy") == ql->head->next);
+        assert(quicklistBookmarkFind(ql, "_missing") == NULL);
+        assert(ql->len==3);
+        quicklistBookmarksClear(ql); /* for coverage */
+        assert(quicklistBookmarkFind(ql, "_dummy") == NULL);
+        quicklistRelease(ql);
+    }
+
+    TEST("bookmark limit") {
+        int i;
+        quicklist *ql = quicklistNew(1, 0);
+        quicklistPushHead(ql, "1", 1);
+        for (i=0; i<QL_MAX_BM; i++)
+            assert(quicklistBookmarkCreate(&ql, genstr("",i), ql->head));
+        /* when all bookmarks are used, creation fails */
+        assert(!quicklistBookmarkCreate(&ql, "_test", ql->head));
+        /* delete one and see that we can now create another */
+        assert(quicklistBookmarkDelete(ql, "0"));
+        assert(quicklistBookmarkCreate(&ql, "_test", ql->head));
+        /* delete one and see that the rest survive */
+        assert(quicklistBookmarkDelete(ql, "_test"));
+        for (i=1; i<QL_MAX_BM; i++)
+            assert(quicklistBookmarkFind(ql, genstr("",i)) == ql->head);
+        /* make sure the deleted ones are indeed gone */
+        assert(!quicklistBookmarkFind(ql, "0"));
+        assert(!quicklistBookmarkFind(ql, "_test"));
+        quicklistRelease(ql);
+    }
+
     if (!err)
         printf("ALL TESTS PASSED!\n");
     else

src/quicklist.h

@@ -28,6 +28,8 @@
  * POSSIBILITY OF SUCH DAMAGE.
  */
 
+#include <stdint.h> // for UINTPTR_MAX
+
 #ifndef __QUICKLIST_H__
 #define __QUICKLIST_H__
 
@@ -64,19 +66,51 @@ typedef struct quicklistLZF {
     char compressed[];
 } quicklistLZF;
 
+/* Bookmarks are padded with realloc at the end of of the quicklist struct.
+ * They should only be used for very big lists if thousands of nodes were the
+ * excess memory usage is negligible, and there's a real need to iterate on them
+ * in portions.
+ * When not used, they don't add any memory overhead, but when used and then
+ * deleted, some overhead remains (to avoid resonance).
+ * The number of bookmarks used should be kept to minimum since it also adds
+ * overhead on node deletion (searching for a bookmark to update). */
+typedef struct quicklistBookmark {
+    quicklistNode *node;
+    char *name;
+} quicklistBookmark;
+
+#if UINTPTR_MAX == 0xffffffff
+/* 32-bit */
+#   define QL_FILL_BITS 14
+#   define QL_COMP_BITS 14
+#   define QL_BM_BITS 4
+#elif UINTPTR_MAX == 0xffffffffffffffff
+/* 64-bit */
+#   define QL_FILL_BITS 16
+#   define QL_COMP_BITS 16
+#   define QL_BM_BITS 4 /* we can encode more, but we rather limit the user
+                           since they cause performance degradation. */
+#else
+#   error unknown arch bits count
+#endif
+
 /* quicklist is a 40 byte struct (on 64-bit systems) describing a quicklist.
  * 'count' is the number of total entries.
  * 'len' is the number of quicklist nodes.
  * 'compress' is: -1 if compression disabled, otherwise it's the number
  *                of quicklistNodes to leave uncompressed at ends of quicklist.
- * 'fill' is the user-requested (or default) fill factor. */
+ * 'fill' is the user-requested (or default) fill factor.
+ * 'bookmakrs are an optional feature that is used by realloc this struct,
+ *      so that they don't consume memory when not used. */
 typedef struct quicklist {
     quicklistNode *head;
     quicklistNode *tail;
     unsigned long count;        /* total count of all entries in all ziplists */
     unsigned long len;          /* number of quicklistNodes */
-    int fill : 16;              /* fill factor for individual nodes */
+    int fill : QL_FILL_BITS;              /* fill factor for individual nodes */
-    unsigned int compress : 16; /* depth of end nodes not to compress;0=off */
+    unsigned int compress : QL_COMP_BITS; /* depth of end nodes not to compress;0=off */
+    unsigned int bookmark_count: QL_BM_BITS;
+    quicklistBookmark bookmarks[];
 } quicklist;
 
 typedef struct quicklistIter {
@@ -158,6 +192,12 @@ unsigned long quicklistCount(const quicklist *ql);
 int quicklistCompare(unsigned char *p1, unsigned char *p2, int p2_len);
 size_t quicklistGetLzf(const quicklistNode *node, void **data);
 
+/* bookmarks */
+int quicklistBookmarkCreate(quicklist **ql_ref, const char *name, quicklistNode *node);
+int quicklistBookmarkDelete(quicklist *ql, const char *name);
+quicklistNode *quicklistBookmarkFind(quicklist *ql, const char *name);
+void quicklistBookmarksClear(quicklist *ql);
+
 #ifdef REDIS_TEST
 int quicklistTest(int argc, char *argv[]);
 #endif

tests/unit/memefficiency.tcl

@@ -209,5 +209,97 @@ start_server {tags {"defrag"}} {
             assert {$digest eq $newdigest}
             r save ;# saving an rdb iterates over all the data / pointers
         } {OK}
+
+        test "Active defrag big list" {
+            r flushdb
+            r config resetstat
+            r config set save "" ;# prevent bgsave from interfereing with save below
+            r config set hz 100
+            r config set activedefrag no
+            r config set active-defrag-max-scan-fields 1000
+            r config set active-defrag-threshold-lower 5
+            r config set active-defrag-cycle-min 65
+            r config set active-defrag-cycle-max 75
+            r config set active-defrag-ignore-bytes 2mb
+            r config set maxmemory 0
+            r config set list-max-ziplist-size 5 ;# list of 500k items will have 100k quicklist nodes
+
+            # create big keys with 10k items
+            set rd [redis_deferring_client]
+
+            set expected_frag 1.7
+            # add a mass of list nodes to two lists (allocations are interlaced)
+            set val [string repeat A 100] ;# 5 items of 100 bytes puts us in the 640 bytes bin, which has 32 regs, so high potential for fragmentation
+            for {set j 0} {$j < 500000} {incr j} {
+                $rd lpush biglist1 $val
+                $rd lpush biglist2 $val
+            }
+            for {set j 0} {$j < 500000} {incr j} {
+                $rd read ; # Discard replies
+                $rd read ; # Discard replies
+            }
+
+            # create some fragmentation
+            r del biglist2
+
+            # start defrag
+            after 120 ;# serverCron only updates the info once in 100ms
+            set frag [s allocator_frag_ratio]
+            if {$::verbose} {
+                puts "frag $frag"
+            }
+
+            assert {$frag >= $expected_frag}
+            r config set latency-monitor-threshold 5
+            r latency reset
+
+            set digest [r debug digest]
+            catch {r config set activedefrag yes} e
+            if {![string match {DISABLED*} $e]} {
+                # wait for the active defrag to start working (decision once a second)
+                wait_for_condition 50 100 {
+                    [s active_defrag_running] ne 0
+                } else {
+                    fail "defrag not started."
+                }
+
+                # wait for the active defrag to stop working
+                wait_for_condition 500 100 {
+                    [s active_defrag_running] eq 0
+                } else {
+                    after 120 ;# serverCron only updates the info once in 100ms
+                    puts [r info memory]
+                    puts [r info stats]
+                    puts [r memory malloc-stats]
+                    fail "defrag didn't stop."
+                }
+
+                # test the the fragmentation is lower
+                after 120 ;# serverCron only updates the info once in 100ms
+                set frag [s allocator_frag_ratio]
+                set max_latency 0
+                foreach event [r latency latest] {
+                    lassign $event eventname time latency max
+                    if {$eventname == "active-defrag-cycle"} {
+                        set max_latency $max
+                    }
+                }
+                if {$::verbose} {
+                    puts "frag $frag"
+                    puts "max latency $max_latency"
+                    puts [r latency latest]
+                    puts [r latency history active-defrag-cycle]
+                }
+                assert {$frag < 1.1}
+                # due to high fragmentation, 100hz, and active-defrag-cycle-max set to 75,
+                # we expect max latency to be not much higher than 7.5ms
+                assert {$max_latency <= 12}
+            }
+            # verify the data isn't corrupted or changed
+            set newdigest [r debug digest]
+            assert {$digest eq $newdigest}
+            r save ;# saving an rdb iterates over all the data / pointers
+            r del biglist1 ;# coverage for quicklistBookmarksClear
+        } {1}
     }
 }