在 pg v11 和 v12 上 常见测试用例
CREATE TABLE rel ( a bigint NOT NULL, b bigint NOT NULL ); ALTER TABLE rel ADD CONSTRAINT rel_pkey PRIMARY KEY (a, b); CREATE INDEX rel_b_idx ON rel (b); \d rel Table "public.rel" Column | Type | Collation | Nullable | Default --------+--------+-----------+----------+--------- a | bigint | | not null | b | bigint | | not null | Indexes: "rel_pkey" PRIMARY KEY, btree (a, b) "rel_b_idx" btree (b)
- 它确保“a”和“b” 两字段的每种组合最多有一个条目。
- 它可以加快与给定“b”相关的所有“a”的搜索速度。
加入测试数据
INSERT INTO rel (a, b) SELECT i, i / 10000 FROM generate_series(1, 20000000) AS i; /* 收集统计信息 */ VACUUM (ANALYZE) rel;
B-tree索引提高1：插入很多重复的索引和数值
当我们比较的b列索引的大小的第一个区别是显而易见的：
v11: \di+ rel_b_idx List of relations Schema | Name | Type | Owner | Table | Size | Description --------+-------------+-------+----------+-------+--------+------------- public | rel_b_idx | index | postgres | rel | 545 MB | (1 row)
v12: \di+ rel_b_idx Schema | Name | Type | Owner | Table | Size | Description --------+-------------+-------+----------+-------+--------+------------- public | rel_b_idx | index | postgres | rel | 408 MB | (1 row)
v11 比 v12 还要大 33%
每一个b列在index发生10000次，因此会有很多叶子节点的所有密钥是相同的（每个叶子节点可以包含几百项）。
V12之前，叶子页必须是分立的，有时是最右边的叶子节点，但有时不是。最右边的叶子节点总是朝着右端，
以优化单调递增插入拆分。与此相反，其他叶子节点是在中间，其中浪费的空间分割。
与V12，该表的行的物理地址（“元组ID”或TID）是索引关键字的一部分，所以重复的索引条目存储在表的顺序。
这会造成这样的条目索引扫描访问的物理顺序表，它可以是一个显著的性能优势，特别是在机械磁盘。
换句话说，重复索引条目的相关性将是完美的。而且，仅由重复的页将在右端分裂，产生密集索引。
加入类似的优化多列索引，但它并不适用于我们的主键索引，因为重复不是在第1列。
主键索引在V11和V12紧凑，因为第一列是单调递增的，所以叶页拆分在最右边的页面总是发生。
PostgreSQL的已经有针对的优化。
B-tree索引提高2：内部索引页面的压缩存储
对于主键索引的改进是不那么明显，因为它们几乎在尺寸在V11和V12相同。我们必须更深入的挖掘这里。
首先，观察指标，只有在这两个V11和V12（块缓存）扫描：
在v11: EXPLAIN (ANALYZE, BUFFERS, COSTS off, SUMMARY off, TIMING off) S SELECT a, b FROM rel W WHERE a = 420024 AND b = 42; QUERY PLAN - --------------------------------------------------------------- Index Only Scan using rel_pkey on rel (actual rows=1 loops=1) Index Cond: ((a = 420024) AND (b = 42)) Heap Fetches: 0 Buffers: shared hit=5 ( (4 rows) 在v12: EXPLAIN (ANALYZE, BUFFERS, COSTS off, SUMMARY off, TIMING off) S SELECT a, b FROM rel W WHERE a = 420024 AND b = 42; QUERY PLAN - --------------------------------------------------------------- Index Only Scan using rel_pkey on rel (actual rows=1 loops=1) Index Cond: ((a = 420024) AND (b = 42)) Heap Fetches: 0 Buffers: shared hit=4 ( (4 rows)
在v12中，将读取少一（索引）的块，这意味着该索引少一级。
由于索引的大小几乎相同，因此必须意味着内部页面可以容纳更多的索引条目。
在v12中，索引具有更大的扇出度。
如上所述，PostgreSQL的V12引入的TID作为索引关键字，这会浪费在内部索引页的空间过多量的一部分。
所以同一个commit引入的来自内部 Page “冗余”索引属性。该TID是多余的，
因为是从包含子句非键属性（V11这些也从内部索引页除去）。
不过，PostgreSQL的V12也可以截断不需要的表行识别这些指标的属性。
在我们的主键索引，出价是一个冗余列，并从内部索引页，
从而节省了8个字节的每个索引条目空间。让我们一起来看看与pageinspect扩展内部索引页：
在 v11: SELECT * FROM bt_page_items('rel_pkey', 2550); itemoffset | ctid | itemlen | nulls | vars | data - ------------+------------+---------+-------+------+------------------------------------------------- 1 | (2667,88) | 24 | f | f | cd 8f 0a 00 00 00 00 00 45 00 00 00 00 00 00 00 2 | (2462,0) | 8 | f | f | 3 | (2463,15) | 24 | f | f | d6 c0 09 00 00 00 00 00 3f 00 00 00 00 00 00 00 4 | (2464,91) | 24 | f | f | db c1 09 00 00 00 00 00 3f 00 00 00 00 00 00 00 5 | (2465,167) | 24 | f | f | e0 c2 09 00 00 00 00 00 3f 00 00 00 00 00 00 00 6 | (2466,58) | 24 | f | f | e5 c3 09 00 00 00 00 00 3f 00 00 00 00 00 00 00 7 | (2467,134) | 24 | f | f | ea c4 09 00 00 00 00 00 40 00 00 00 00 00 00 00 8 | (2468,25) | 24 | f | f | ef c5 09 00 00 00 00 00 40 00 00 00 00 00 00 00 9 | (2469,101) | 24 | f | f | f4 c6 09 00 00 00 00 00 40 00 00 00 00 00 00 00 10 | (2470,177) | 24 | f | f | f9 c7 09 00 00 00 00 00 40 00 00 00 00 00 00 00 . ... 205 | (2666,12) | 24 | f | f | c8 8e 0a 00 00 00 00 00 45 00 00 00 00 00 00 00 ( (205 rows) 在数据输入我们所看到的援助和出价字节。该实验在 little-endian 机器上进行的， 所以在第6行的数目将是0x09C3E5和0x3F的或（十进制数）639973和63.每个索引条目是24个字节宽，这8个字节是所述元组报头。 在 v12: SELECT * FROM bt_page_items('rel_pkey', 2700); itemoffset | ctid | itemlen | nulls | vars | data - ------------+----------+---------+-------+------+------------------------- 1 | (2862,1) | 16 | f | f | ab 59 0b 00 00 00 00 00 2 | (2576,0) | 8 | f | f | 3 | (2577,1) | 16 | f | f | 1f 38 0a 00 00 00 00 00 4 | (2578,1) | 16 | f | f | 24 39 0a 00 00 00 00 00 5 | (2579,1) | 16 | f | f | 29 3a 0a 00 00 00 00 00 6 | (2580,1) | 16 | f | f | 2e 3b 0a 00 00 00 00 00 7 | (2581,1) | 16 | f | f | 33 3c 0a 00 00 00 00 00 8 | (2582,1) | 16 | f | f | 38 3d 0a 00 00 00 00 00 9 | (2583,1) | 16 | f | f | 3d 3e 0a 00 00 00 00 00 10 | (2584,1) | 16 | f | f | 42 3f 0a 00 00 00 00 00 . ... 286 | (2861,1) | 16 | f | f | a6 58 0b 00 00 00 00 00 ( (286 rows)
该数据仅包含a列，因为a列已经被截断了。这减少了索引项的大小为16，让更多的条目适合索引页上。
升级注意事项
由于索引存储在V12被改变，新的B-tree索引第4版已经推出。
由于与pg_upgrade不改变数据文件升级，索引仍然会在3.0版本升级后。
PostgreSQL的V12可以使用这些指标，但上述的优化将不可用。
你需要重新索引的索引将其升级到4.0版本（这已经在PostgreSQL的V12变得更加容易与REINDEX兼）。
其他B-tree索引功能在推出V12
有PostgreSQL中V12添加了一些其他方面的改进。如下简单列表：
1. 减少B树索引插入，以提高性能锁定开销。
2. REINDEX CONCURRENTLY，重建无停机时间的索引。
3. 完善与许多属性的索引仅索引扫描性能。
4. 添加视图 pg_stat_progress_create_index 报到CREATE INDEX和REINDEX进展。
补充一下btree version4代码
/* * lib/btree.c - Simple In-memory B+Tree * * As should be obvious for Linux kernel code, license is GPLv2 * * Copyright (c) 2007-2008 Joern Engel <joern@purestorage.com> * Bits and pieces stolen from Peter Zijlstra's code, which is * Copyright 2007, Red Hat Inc. Peter Zijlstra * GPLv2 * * see http://programming.kicks-ass.net/kernel-patches/vma_lookup/btree.patch * * A relatively simple B+Tree implementation. I have written it as a learning * exercise to understand how B+Trees work. Turned out to be useful as well. * * B+Trees can be used similar to Linux radix trees (which don't have anything * in common with textbook radix trees, beware). Prerequisite for them working * well is that access to a random tree node is much faster than a large number * of operations within each node. * * Disks have fulfilled the prerequisite for a long time. More recently DRAM * has gained similar properties, as memory access times, when measured in cpu * cycles, have increased. Cacheline sizes have increased as well, which also * helps B+Trees. * * Compared to radix trees, B+Trees are more efficient when dealing with a * sparsely populated address space. Between 25% and 50% of the memory is * occupied with valid pointers. When densely populated, radix trees contain * ~98% pointers - hard to beat. Very sparse radix trees contain only ~2% * pointers. * * This particular implementation stores pointers identified by a long value. * Storing NULL pointers is illegal, lookup will return NULL when no entry * was found. * * A tricks was used that is not commonly found in textbooks. The lowest * values are to the right, not to the left. All used slots within a node * are on the left, all unused slots contain NUL values. Most operations * simply loop once over all slots and terminate on the first NUL. */ #include <linux/btree.h> #include <linux/cache.h> #include <linux/kernel.h> #include <linux/slab.h> #include <linux/module.h> #define MAX(a, b) ((a) > (b) ? (a) : (b)) #define NODESIZE MAX(L1_CACHE_BYTES, 128) struct btree_geo { int keylen; int no_pairs; int no_longs; }; struct btree_geo btree_geo32 = { .keylen = 1, .no_pairs = NODESIZE / sizeof(long) / 2, .no_longs = NODESIZE / sizeof(long) / 2, }; EXPORT_SYMBOL_GPL(btree_geo32); #define LONG_PER_U64 (64 / BITS_PER_LONG) struct btree_geo btree_geo64 = { .keylen = LONG_PER_U64, .no_pairs = NODESIZE / sizeof(long) / (1 + LONG_PER_U64), .no_longs = LONG_PER_U64 * (NODESIZE / sizeof(long) / (1 + LONG_PER_U64)), }; EXPORT_SYMBOL_GPL(btree_geo64); struct btree_geo btree_geo128 = { .keylen = 2 * LONG_PER_U64, .no_pairs = NODESIZE / sizeof(long) / (1 + 2 * LONG_PER_U64), .no_longs = 2 * LONG_PER_U64 * (NODESIZE / sizeof(long) / (1 + 2 * LONG_PER_U64)), }; EXPORT_SYMBOL_GPL(btree_geo128); #define MAX_KEYLEN (2 * LONG_PER_U64) static struct kmem_cache *btree_cachep; void *btree_alloc(gfp_t gfp_mask, void *pool_data) { return kmem_cache_alloc(btree_cachep, gfp_mask); } EXPORT_SYMBOL_GPL(btree_alloc); void btree_free(void *element, void *pool_data) { kmem_cache_free(btree_cachep, element); } EXPORT_SYMBOL_GPL(btree_free); static unsigned long *btree_node_alloc(struct btree_head *head, gfp_t gfp) { unsigned long *node; node = mempool_alloc(head->mempool, gfp); if (likely(node)) memset(node, 0, NODESIZE); return node; } static int longcmp(const unsigned long *l1, const unsigned long *l2, size_t n) { size_t i; for (i = 0; i < n; i++) { if (l1[i] < l2[i]) return -1; if (l1[i] > l2[i]) return 1; } return 0; } static unsigned long *longcpy(unsigned long *dest, const unsigned long *src, size_t n) { size_t i; for (i = 0; i < n; i++) dest[i] = src[i]; return dest; } static unsigned long *longset(unsigned long *s, unsigned long c, size_t n) { size_t i; for (i = 0; i < n; i++) s[i] = c; return s; } static void dec_key(struct btree_geo *geo, unsigned long *key) { unsigned long val; int i; for (i = geo->keylen - 1; i >= 0; i--) { val = key[i]; key[i] = val - 1; if (val) break; } } static unsigned long *bkey(struct btree_geo *geo, unsigned long *node, int n) { return &node[n * geo->keylen]; } static void *bval(struct btree_geo *geo, unsigned long *node, int n) { return (void *)node[geo->no_longs + n]; } static void setkey(struct btree_geo *geo, unsigned long *node, int n, unsigned long *key) { longcpy(bkey(geo, node, n), key, geo->keylen); } static void setval(struct btree_geo *geo, unsigned long *node, int n, void *val) { node[geo->no_longs + n] = (unsigned long) val; } static void clearpair(struct btree_geo *geo, unsigned long *node, int n) { longset(bkey(geo, node, n), 0, geo->keylen); node[geo->no_longs + n] = 0; } static inline void __btree_init(struct btree_head *head) { head->node = NULL; head->height = 0; } void btree_init_mempool(struct btree_head *head, mempool_t *mempool) { __btree_init(head); head->mempool = mempool; } EXPORT_SYMBOL_GPL(btree_init_mempool); int btree_init(struct btree_head *head) { __btree_init(head); head->mempool = mempool_create(0, btree_alloc, btree_free, NULL); if (!head->mempool) return -ENOMEM; return 0; } EXPORT_SYMBOL_GPL(btree_init); void btree_destroy(struct btree_head *head) { mempool_free(head->node, head->mempool); mempool_destroy(head->mempool); head->mempool = NULL; } EXPORT_SYMBOL_GPL(btree_destroy); void *btree_last(struct btree_head *head, struct btree_geo *geo, unsigned long *key) { int height = head->height; unsigned long *node = head->node; if (height == 0) return NULL; for ( ; height > 1; height--) node = bval(geo, node, 0); longcpy(key, bkey(geo, node, 0), geo->keylen); return bval(geo, node, 0); } EXPORT_SYMBOL_GPL(btree_last); static int keycmp(struct btree_geo *geo, unsigned long *node, int pos, unsigned long *key) { return longcmp(bkey(geo, node, pos), key, geo->keylen); } static int keyzero(struct btree_geo *geo, unsigned long *key) { int i; for (i = 0; i < geo->keylen; i++) if (key[i]) return 0; return 1; } void *btree_lookup(struct btree_head *head, struct btree_geo *geo, unsigned long *key) { int i, height = head->height; unsigned long *node = head->node; if (height == 0) return NULL; for ( ; height > 1; height--) { for (i = 0; i < geo->no_pairs; i++) if (keycmp(geo, node, i, key) <= 0) break; if (i == geo->no_pairs) return NULL; node = bval(geo, node, i); if (!node) return NULL; } if (!node) return NULL; for (i = 0; i < geo->no_pairs; i++) if (keycmp(geo, node, i, key) == 0) return bval(geo, node, i); return NULL; } EXPORT_SYMBOL_GPL(btree_lookup); int btree_update(struct btree_head *head, struct btree_geo *geo, unsigned long *key, void *val) { int i, height = head->height; unsigned long *node = head->node; if (height == 0) return -ENOENT; for ( ; height > 1; height--) { for (i = 0; i < geo->no_pairs; i++) if (keycmp(geo, node, i, key) <= 0) break; if (i == geo->no_pairs) return -ENOENT; node = bval(geo, node, i); if (!node) return -ENOENT; } if (!node) return -ENOENT; for (i = 0; i < geo->no_pairs; i++) if (keycmp(geo, node, i, key) == 0) { setval(geo, node, i, val); return 0; } return -ENOENT; } EXPORT_SYMBOL_GPL(btree_update); /* * Usually this function is quite similar to normal lookup. But the key of * a parent node may be smaller than the smallest key of all its siblings. * In such a case we cannot just return NULL, as we have only proven that no * key smaller than __key, but larger than this parent key exists. * So we set __key to the parent key and retry. We have to use the smallest * such parent key, which is the last parent key we encountered. */ void *btree_get_prev(struct btree_head *head, struct btree_geo *geo, unsigned long *__key) { int i, height; unsigned long *node, *oldnode; unsigned long *retry_key = NULL, key[MAX_KEYLEN]; if (keyzero(geo, __key)) return NULL; if (head->height == 0) return NULL; longcpy(key, __key, geo->keylen); retry: dec_key(geo, key); node = head->node; for (height = head->height ; height > 1; height--) { for (i = 0; i < geo->no_pairs; i++) if (keycmp(geo, node, i, key) <= 0) break; if (i == geo->no_pairs) goto miss; oldnode = node; node = bval(geo, node, i); if (!node) goto miss; retry_key = bkey(geo, oldnode, i); } if (!node) goto miss; for (i = 0; i < geo->no_pairs; i++) { if (keycmp(geo, node, i, key) <= 0) { if (bval(geo, node, i)) { longcpy(__key, bkey(geo, node, i), geo->keylen); return bval(geo, node, i); } else goto miss; } } miss: if (retry_key) { longcpy(key, retry_key, geo->keylen); retry_key = NULL; goto retry; } return NULL; } EXPORT_SYMBOL_GPL(btree_get_prev); static int getpos(struct btree_geo *geo, unsigned long *node, unsigned long *key) { int i; for (i = 0; i < geo->no_pairs; i++) { if (keycmp(geo, node, i, key) <= 0) break; } return i; } static int getfill(struct btree_geo *geo, unsigned long *node, int start) { int i; for (i = start; i < geo->no_pairs; i++) if (!bval(geo, node, i)) break; return i; } /* * locate the correct leaf node in the btree */ static unsigned long *find_level(struct btree_head *head, struct btree_geo *geo, unsigned long *key, int level) { unsigned long *node = head->node; int i, height; for (height = head->height; height > level; height--) { for (i = 0; i < geo->no_pairs; i++) if (keycmp(geo, node, i, key) <= 0) break; if ((i == geo->no_pairs) || !bval(geo, node, i)) { /* right-most key is too large, update it */ /* FIXME: If the right-most key on higher levels is * always zero, this wouldn't be necessary. */ i--; setkey(geo, node, i, key); } BUG_ON(i < 0); node = bval(geo, node, i); } BUG_ON(!node); return node; } static int btree_grow(struct btree_head *head, struct btree_geo *geo, gfp_t gfp) { unsigned long *node; int fill; node = btree_node_alloc(head, gfp); if (!node) return -ENOMEM; if (head->node) { fill = getfill(geo, head->node, 0); setkey(geo, node, 0, bkey(geo, head->node, fill - 1)); setval(geo, node, 0, head->node); } head->node = node; head->height++; return 0; } static void btree_shrink(struct btree_head *head, struct btree_geo *geo) { unsigned long *node; int fill; if (head->height <= 1) return; node = head->node; fill = getfill(geo, node, 0); BUG_ON(fill > 1); head->node = bval(geo, node, 0); head->height--; mempool_free(node, head->mempool); } static int btree_insert_level(struct btree_head *head, struct btree_geo *geo, unsigned long *key, void *val, int level, gfp_t gfp) { unsigned long *node; int i, pos, fill, err; BUG_ON(!val); if (head->height < level) { err = btree_grow(head, geo, gfp); if (err) return err; } retry: node = find_level(head, geo, key, level); pos = getpos(geo, node, key); fill = getfill(geo, node, pos); /* two identical keys are not allowed */ BUG_ON(pos < fill && keycmp(geo, node, pos, key) == 0); if (fill == geo->no_pairs) { /* need to split node */ unsigned long *new; new = btree_node_alloc(head, gfp); if (!new) return -ENOMEM; err = btree_insert_level(head, geo, bkey(geo, node, fill / 2 - 1), new, level + 1, gfp); if (err) { mempool_free(new, head->mempool); return err; } for (i = 0; i < fill / 2; i++) { setkey(geo, new, i, bkey(geo, node, i)); setval(geo, new, i, bval(geo, node, i)); setkey(geo, node, i, bkey(geo, node, i + fill / 2)); setval(geo, node, i, bval(geo, node, i + fill / 2)); clearpair(geo, node, i + fill / 2); } if (fill & 1) { setkey(geo, node, i, bkey(geo, node, fill - 1)); setval(geo, node, i, bval(geo, node, fill - 1)); clearpair(geo, node, fill - 1); } goto retry; } BUG_ON(fill >= geo->no_pairs); /* shift and insert */ for (i = fill; i > pos; i--) { setkey(geo, node, i, bkey(geo, node, i - 1)); setval(geo, node, i, bval(geo, node, i - 1)); } setkey(geo, node, pos, key); setval(geo, node, pos, val); return 0; } int btree_insert(struct btree_head *head, struct btree_geo *geo, unsigned long *key, void *val, gfp_t gfp) { BUG_ON(!val); return btree_insert_level(head, geo, key, val, 1, gfp); } EXPORT_SYMBOL_GPL(btree_insert); static void *btree_remove_level(struct btree_head *head, struct btree_geo *geo, unsigned long *key, int level); static void merge(struct btree_head *head, struct btree_geo *geo, int level, unsigned long *left, int lfill, unsigned long *right, int rfill, unsigned long *parent, int lpos) { int i; for (i = 0; i < rfill; i++) { /* Move all keys to the left */ setkey(geo, left, lfill + i, bkey(geo, right, i)); setval(geo, left, lfill + i, bval(geo, right, i)); } /* Exchange left and right child in parent */ setval(geo, parent, lpos, right); setval(geo, parent, lpos + 1, left); /* Remove left (formerly right) child from parent */ btree_remove_level(head, geo, bkey(geo, parent, lpos), level + 1); mempool_free(right, head->mempool); } static void rebalance(struct btree_head *head, struct btree_geo *geo, unsigned long *key, int level, unsigned long *child, int fill) { unsigned long *parent, *left = NULL, *right = NULL; int i, no_left, no_right; if (fill == 0) { /* Because we don't steal entries from a neighbour, this case * can happen. Parent node contains a single child, this * node, so merging with a sibling never happens. */ btree_remove_level(head, geo, key, level + 1); mempool_free(child, head->mempool); return; } parent = find_level(head, geo, key, level + 1); i = getpos(geo, parent, key); BUG_ON(bval(geo, parent, i) != child); if (i > 0) { left = bval(geo, parent, i - 1); no_left = getfill(geo, left, 0); if (fill + no_left <= geo->no_pairs) { merge(head, geo, level, left, no_left, child, fill, parent, i - 1); return; } } if (i + 1 < getfill(geo, parent, i)) { right = bval(geo, parent, i + 1); no_right = getfill(geo, right, 0); if (fill + no_right <= geo->no_pairs) { merge(head, geo, level, child, fill, right, no_right, parent, i); return; } } /* * We could also try to steal one entry from the left or right * neighbor. By not doing so we changed the invariant from * "all nodes are at least half full" to "no two neighboring * nodes can be merged". Which means that the average fill of * all nodes is still half or better. */ } static void *btree_remove_level(struct btree_head *head, struct btree_geo *geo, unsigned long *key, int level) { unsigned long *node; int i, pos, fill; void *ret; if (level > head->height) { /* we recursed all the way up */ head->height = 0; head->node = NULL; return NULL; } node = find_level(head, geo, key, level); pos = getpos(geo, node, key); fill = getfill(geo, node, pos); if ((level == 1) && (keycmp(geo, node, pos, key) != 0)) return NULL; ret = bval(geo, node, pos); /* remove and shift */ for (i = pos; i < fill - 1; i++) { setkey(geo, node, i, bkey(geo, node, i + 1)); setval(geo, node, i, bval(geo, node, i + 1)); } clearpair(geo, node, fill - 1); if (fill - 1 < geo->no_pairs / 2) { if (level < head->height) rebalance(head, geo, key, level, node, fill - 1); else if (fill - 1 == 1) btree_shrink(head, geo); } return ret; } void *btree_remove(struct btree_head *head, struct btree_geo *geo, unsigned long *key) { if (head->height == 0) return NULL; return btree_remove_level(head, geo, key, 1); } EXPORT_SYMBOL_GPL(btree_remove); int btree_merge(struct btree_head *target, struct btree_head *victim, struct btree_geo *geo, gfp_t gfp) { unsigned long key[MAX_KEYLEN]; unsigned long dup[MAX_KEYLEN]; void *val; int err; BUG_ON(target == victim); if (!(target->node)) { /* target is empty, just copy fields over */ target->node = victim->node; target->height = victim->height; __btree_init(victim); return 0; } /* TODO: This needs some optimizations. Currently we do three tree * walks to remove a single object from the victim. */ for (;;) { if (!btree_last(victim, geo, key)) break; val = btree_lookup(victim, geo, key); err = btree_insert(target, geo, key, val, gfp); if (err) return err; /* We must make a copy of the key, as the original will get * mangled inside btree_remove. */ longcpy(dup, key, geo->keylen); btree_remove(victim, geo, dup); } return 0; } EXPORT_SYMBOL_GPL(btree_merge); static size_t __btree_for_each(struct btree_head *head, struct btree_geo *geo, unsigned long *node, unsigned long opaque, void (*func)(void *elem, unsigned long opaque, unsigned long *key, size_t index, void *func2), void *func2, int reap, int height, size_t count) { int i; unsigned long *child; for (i = 0; i < geo->no_pairs; i++) { child = bval(geo, node, i); if (!child) break; if (height > 1) count = __btree_for_each(head, geo, child, opaque, func, func2, reap, height - 1, count); else func(child, opaque, bkey(geo, node, i), count++, func2); } if (reap) mempool_free(node, head->mempool); return count; } static void empty(void *elem, unsigned long opaque, unsigned long *key, size_t index, void *func2) { } void visitorl(void *elem, unsigned long opaque, unsigned long *key, size_t index, void *__func) { visitorl_t func = __func; func(elem, opaque, *key, index); } EXPORT_SYMBOL_GPL(visitorl); void visitor32(void *elem, unsigned long opaque, unsigned long *__key, size_t index, void *__func) { visitor32_t func = __func; u32 *key = (void *)__key; func(elem, opaque, *key, index); } EXPORT_SYMBOL_GPL(visitor32); void visitor64(void *elem, unsigned long opaque, unsigned long *__key, size_t index, void *__func) { visitor64_t func = __func; u64 *key = (void *)__key; func(elem, opaque, *key, index); } EXPORT_SYMBOL_GPL(visitor64); void visitor128(void *elem, unsigned long opaque, unsigned long *__key, size_t index, void *__func) { visitor128_t func = __func; u64 *key = (void *)__key; func(elem, opaque, key[0], key[1], index); } EXPORT_SYMBOL_GPL(visitor128); size_t btree_visitor(struct btree_head *head, struct btree_geo *geo, unsigned long opaque, void (*func)(void *elem, unsigned long opaque, unsigned long *key, size_t index, void *func2), void *func2) { size_t count = 0; if (!func2) func = empty; if (head->node) count = __btree_for_each(head, geo, head->node, opaque, func, func2, 0, head->height, 0); return count; } EXPORT_SYMBOL_GPL(btree_visitor); size_t btree_grim_visitor(struct btree_head *head, struct btree_geo *geo, unsigned long opaque, void (*func)(void *elem, unsigned long opaque, unsigned long *key, size_t index, void *func2), void *func2) { size_t count = 0; if (!func2) func = empty; if (head->node) count = __btree_for_each(head, geo, head->node, opaque, func, func2, 1, head->height, 0); __btree_init(head); return count; } EXPORT_SYMBOL_GPL(btree_grim_visitor); static int __init btree_module_init(void) { btree_cachep = kmem_cache_create("btree_node", NODESIZE, 0, SLAB_HWCACHE_ALIGN, NULL); return 0; } static void __exit btree_module_exit(void) { kmem_cache_destroy(btree_cachep); } /* If core code starts using btree, initialization should happen even earlier */ module_init(btree_module_init); module_exit(btree_module_exit); MODULE_AUTHOR("Joern Engel <joern@logfs.org>"); MODULE_AUTHOR("Johannes Berg <johannes@sipsolutions.net>"); MODULE_LICENSE("GPL");
总结
拥有许多重复的条目索引, V12 更有优势 , 推荐 pg_upgrade后用 REINDEX CONCURRENTLY 重新索引。
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