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itemprop=author itemscope itemtype=http://schema.org/Person><meta content=/uploads/avatar.jpg itemprop=image><meta content=Nicksxs itemprop=name></span><span hidden itemprop=publisher itemscope itemtype=http://schema.org/Organization><meta content="Nicksxs's Blog" itemprop=name><meta content="Nicksxs 的技术博客,深入 Java 运行时与生产诊断、低成本大模型推理和 Agent 工程实践。" itemprop=description></span><span hidden itemprop=post itemscope itemtype=http://schema.org/CreativeWork><meta content="redis数据结构介绍六 快表 | Nicksxs's Blog" itemprop=name><meta content="这应该是 redis 系列的最后一篇了,讲下快表,其实最前面讲的链表在早先的 redis 版本中也作为 list 的数据结构使用过,但是单纯的链表的缺陷之前也说了,插入便利,但是空间利用率低,并且不能进行二分查找等,检索效率低,ziplist 压缩表的产生也是同理,希望获得更好…" itemprop=description></span><header class=post-header><h1 itemprop="name headline" class=post-title>redis数据结构介绍六 快表</h1><div class=post-meta-container><div class=post-meta><span class=post-meta-item><span class=post-meta-item-icon><i class="far fa-calendar"></i> </span><span class=post-meta-item-text>发表于</span> <time itemprop="dateCreated datePublished" title="创建时间:2020-01-22 21:51:30" datetime=2020-01-22T21:51:30+08:00>2020-01-22</time> </span><span class=post-meta-item><span class=post-meta-item-icon><i class="far fa-folder"></i> </span><span class=post-meta-item-text>分类于</span> <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/Redis/ itemprop=url rel=index><span itemprop=name>Redis</span></a> </span>, <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/Redis/%E6%95%B0%E6%8D%AE%E7%BB%93%E6%9E%84/ itemprop=url rel=index><span itemprop=name>数据结构</span></a> </span>, <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/C/ itemprop=url rel=index><span itemprop=name>C</span></a> </span>, <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/Redis/%E6%BA%90%E7%A0%81/ itemprop=url rel=index><span itemprop=name>源码</span></a> </span>, <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/C/Redis/ itemprop=url rel=index><span itemprop=name>Redis</span></a> </span></span><span class="post-meta-item cloudflare-page-counter" data-title="redis数据结构介绍六 快表" data-increment=true data-path=/2020/01/22/redis%E6%95%B0%E6%8D%AE%E7%BB%93%E6%9E%84%E4%BB%8B%E7%BB%8D%E5%85%AD/ title=阅读次数><span class=post-meta-item-icon><i class="far fa-eye"></i> </span><span class=post-meta-item-text>阅读次数:</span> <span class=cloudflare-page-counter-count></span></span></div><div class=post-description>这应该是 redis 系列的最后一篇了,讲下快表,其实最前面讲的链表在早先的 redis 版本中也作为 list 的数据结构使用过,但是单纯的链表的缺陷之前也说了,插入便利,但是空间利用率低,并且不能进行二分查找等,检索效率低,ziplist 压缩表的产生也是同理,希望获得更好…</div></div></header><div class=post-body itemprop=articleBody><p>这应该是 redis 系列的最后一篇了,讲下快表,其实最前面讲的链表在早先的 redis 版本中也作为 list 的数据结构使用过,但是单纯的链表的缺陷之前也说了,插入便利,但是空间利用率低,并且不能进行二分查找等,检索效率低,ziplist 压缩表的产生也是同理,希望获得更好的性能,包括存储空间和访问性能等,原来我也不懂这个快表要怎么快,然后明白了一个道理,其实并没有什么银弹,只是大牛们会在适合的时候使用最适合的数据结构来实现性能的最大化,这里面有一招就是不同数据结构的组合调整,比如 Java 中的 HashMap,在链表节点数大于 8 时会转变成红黑树,以此提高访问效率,不费话了,回到快表,quicklist,这个数据结构主要使用在 list 类型中,如果我说其实这个 quicklist 就是个链表,可能大家不太会相信,但是事实上的确可以认为 quicklist 是个双向链表,看下代码<figure class="highlight c"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br><span class=line>5</span><br><span class=line>6</span><br><span class=line>7</span><br><span class=line>8</span><br><span class=line>9</span><br><span class=line>10</span><br><span class=line>11</span><br><span class=line>12</span><br><span class=line>13</span><br><span class=line>14</span><br><span class=line>15</span><br><span class=line>16</span><br><span class=line>17</span><br><span class=line>18</span><br><span class=line>19</span><br><span class=line>20</span><br><span class=line>21</span><br><span class=line>22</span><br><span class=line>23</span><br><span class=line>24</span><br><span class=line>25</span><br><span class=line>26</span><br><span class=line>27</span><br><span class=line>28</span><br><span class=line>29</span><br><span class=line>30</span><br><span class=line>31</span><br><span class=line>32</span><br><span class=line>33</span><br><span class=line>34</span><br><span class=line>35</span><br><span class=line>36</span><br><span class=line>37</span><br><span class=line>38</span><br><span class=line>39</span><br><span class=line>40</span><br><span class=line>41</span><br><span class=line>42</span><br><span class=line>43</span><br><span class=line>44</span><br><span class=line>45</span><br></pre><td class=code><pre><span class=line><span class=comment>/* quicklistNode is a 32 byte struct describing a ziplist for a quicklist.</span></span><br><span class=line><span class=comment> * We use bit fields keep the quicklistNode at 32 bytes.</span></span><br><span class=line><span class=comment> * count: 16 bits, max 65536 (max zl bytes is 65k, so max count actually < 32k).</span></span><br><span class=line><span class=comment> * encoding: 2 bits, RAW=1, LZF=2.</span></span><br><span class=line><span class=comment> * container: 2 bits, NONE=1, ZIPLIST=2.</span></span><br><span class=line><span class=comment> * recompress: 1 bit, bool, true if node is temporarry decompressed for usage.</span></span><br><span class=line><span class=comment> * attempted_compress: 1 bit, boolean, used for verifying during testing.</span></span><br><span class=line><span class=comment> * extra: 10 bits, free for future use; pads out the remainder of 32 bits */</span></span><br><span class=line><span class=keyword>typedef</span> <span class=class><span class=keyword>struct</span> <span class=title>quicklistNode</span> {</span></span><br><span class=line> <span class=class><span class=keyword>struct</span> <span class=title>quicklistNode</span> *<span class=title>prev</span>;</span></span><br><span class=line> <span class=class><span class=keyword>struct</span> <span class=title>quicklistNode</span> *<span class=title>next</span>;</span></span><br><span class=line> <span class=type>unsigned</span> <span class=type>char</span> *zl;</span><br><span class=line> <span class=type>unsigned</span> <span class=type>int</span> sz; <span class=comment>/* ziplist size in bytes */</span></span><br><span class=line> <span class=type>unsigned</span> <span class=type>int</span> count : <span class=number>16</span>; <span class=comment>/* count of items in ziplist */</span></span><br><span class=line> <span class=type>unsigned</span> <span class=type>int</span> encoding : <span class=number>2</span>; <span class=comment>/* RAW==1 or LZF==2 */</span></span><br><span class=line> <span class=type>unsigned</span> <span class=type>int</span> container : <span class=number>2</span>; <span class=comment>/* NONE==1 or ZIPLIST==2 */</span></span><br><span class=line> <span class=type>unsigned</span> <span class=type>int</span> recompress : <span class=number>1</span>; <span class=comment>/* was this node previous compressed? */</span></span><br><span class=line> <span class=type>unsigned</span> <span class=type>int</span> attempted_compress : <span class=number>1</span>; <span class=comment>/* node can't compress; too small */</span></span><br><span class=line> <span class=type>unsigned</span> <span class=type>int</span> extra : <span class=number>10</span>; <span class=comment>/* more bits to steal for future usage */</span></span><br><span class=line>} quicklistNode;</span><br><span class=line></span><br><span class=line><span class=comment>/* quicklistLZF is a 4+N byte struct holding 'sz' followed by 'compressed'.</span></span><br><span class=line><span class=comment> * 'sz' is byte length of 'compressed' field.</span></span><br><span class=line><span class=comment> * 'compressed' is LZF data with total (compressed) length 'sz'</span></span><br><span class=line><span class=comment> * <span class=doctag>NOTE:</span> uncompressed length is stored in quicklistNode->sz.</span></span><br><span class=line><span class=comment> * When quicklistNode->zl is compressed, node->zl points to a quicklistLZF */</span></span><br><span class=line><span class=keyword>typedef</span> <span class=class><span class=keyword>struct</span> <span class=title>quicklistLZF</span> {</span></span><br><span class=line> <span class=type>unsigned</span> <span class=type>int</span> sz; <span class=comment>/* LZF size in bytes*/</span></span><br><span class=line> <span class=type>char</span> compressed[];</span><br><span class=line>} quicklistLZF;</span><br><span class=line></span><br><span class=line><span class=comment>/* quicklist is a 40 byte struct (on 64-bit systems) describing a quicklist.</span></span><br><span class=line><span class=comment> * 'count' is the number of total entries.</span></span><br><span class=line><span class=comment> * 'len' is the number of quicklist nodes.</span></span><br><span class=line><span class=comment> * 'compress' is: -1 if compression disabled, otherwise it's the number</span></span><br><span class=line><span class=comment> * of quicklistNodes to leave uncompressed at ends of quicklist.</span></span><br><span class=line><span class=comment> * 'fill' is the user-requested (or default) fill factor. */</span></span><br><span class=line><span class=keyword>typedef</span> <span class=class><span class=keyword>struct</span> <span class=title>quicklist</span> {</span></span><br><span class=line> quicklistNode *head;</span><br><span class=line> quicklistNode *tail;</span><br><span class=line> <span class=type>unsigned</span> <span class=type>long</span> count; <span class=comment>/* total count of all entries in all ziplists */</span></span><br><span class=line> <span class=type>unsigned</span> <span class=type>long</span> len; <span class=comment>/* number of quicklistNodes */</span></span><br><span class=line> <span class=type>int</span> fill : <span class=number>16</span>; <span class=comment>/* fill factor for individual nodes */</span></span><br><span class=line> <span class=type>unsigned</span> <span class=type>int</span> compress : <span class=number>16</span>; <span class=comment>/* depth of end nodes not to compress;0=off */</span></span><br><span class=line>} quicklist;</span><br></pre></table></figure><p>粗略看下,quicklist 里有 head,tail, quicklistNode里有 prev,next 指针,是不是有链表的基本轮廓了,那么为啥这玩意要称为快表呢,快在哪,关键就在这个<code>unsigned char *zl;</code>zl 是不是前面又看到过,就是 ziplist ,这是什么鬼,链表里用压缩表,这不套娃么,先别急,回顾下前面说的 ziplist,ziplist 有哪些特点,内存利用率高,可以从表头快速定位到尾节点,节点可以从后往前找,但是有个缺点,就是从中间插入的效率比较低,需要整体往后移,这个其实是普通数组的优化版,但还是有数组的一些劣势,所以要真的快,是不是可以将链表跟数组真的结合起来。<h2 id=ziplist><a class=headerlink href=#ziplist title=ziplist></a>ziplist</h2><p>这里有两个 redis 的配置参数,<code>list-max-ziplist-size</code> 和 <code>list-compress-depth</code>,先来说第一个,既然快表是将链表跟压缩表数组结合起来使用,那么具体怎么用呢,比如我有一个 10 个元素的 list,那具体怎么放,每个 quicklistNode 里放多大的 ziplist,假如每个快表节点的 ziplist 只放一个元素,那么其实这就退化成了一个链表,如果 10 个元素放在一个 quicklistNode 的 ziplist 里,那就退化成了一个 ziplist,所以有了这个 <code>list-max-ziplist-size</code>,而且它还比较牛,能取正负值,当是正值时,对应的就是每个 quicklistNode 的 ziplist 中的元素个数,比如配置了 <code>list-max-ziplist-size = 5</code>,那么我刚才的 10 个元素的 list 就是一个两个 quicklistNode 组成的快表,每个 quicklistNode 中的 ziplist 包含了五个元素,当 <code>list-max-ziplist-size</code>取负值的时候,它限制了 ziplist 的字节数<figure class="highlight plaintext"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br><span class=line>5</span><br><span class=line>6</span><br><span class=line>7</span><br><span class=line>8</span><br><span class=line>9</span><br><span class=line>10</span><br><span class=line>11</span><br><span class=line>12</span><br><span class=line>13</span><br><span class=line>14</span><br><span class=line>15</span><br><span class=line>16</span><br><span class=line>17</span><br><span class=line>18</span><br><span class=line>19</span><br><span class=line>20</span><br><span class=line>21</span><br><span class=line>22</span><br><span class=line>23</span><br><span class=line>24</span><br><span class=line>25</span><br><span class=line>26</span><br><span class=line>27</span><br></pre><td class=code><pre><span class=line>size_t offset = (-fill) - 1;</span><br><span class=line>if (offset < (sizeof(optimization_level) / sizeof(*optimization_level))) {</span><br><span class=line> if (sz <= optimization_level[offset]) {</span><br><span class=line> return 1;</span><br><span class=line> } else {</span><br><span class=line> return 0;</span><br><span class=line> }</span><br><span class=line>} else {</span><br><span class=line> return 0;</span><br><span class=line>}</span><br><span class=line></span><br><span class=line>/* Optimization levels for size-based filling */</span><br><span class=line>static const size_t optimization_level[] = {4096, 8192, 16384, 32768, 65536};</span><br><span class=line></span><br><span class=line>/* Create a new quicklist.</span><br><span class=line> * Free with quicklistRelease(). */</span><br><span class=line>quicklist *quicklistCreate(void) {</span><br><span class=line> struct quicklist *quicklist;</span><br><span class=line></span><br><span class=line> quicklist = zmalloc(sizeof(*quicklist));</span><br><span class=line> quicklist->head = quicklist->tail = NULL;</span><br><span class=line> quicklist->len = 0;</span><br><span class=line> quicklist->count = 0;</span><br><span class=line> quicklist->compress = 0;</span><br><span class=line> quicklist->fill = -2;</span><br><span class=line> return quicklist;</span><br><span class=line>}</span><br></pre></table></figure><p>这个 fill 就是传进来的 <code>list-max-ziplist-size</code>, 具体对应的就是<ul><li>-5: 每个quicklist节点上的ziplist大小不能超过64 Kb。(注:1kb => 1024 bytes)<li>-4: 每个quicklist节点上的ziplist大小不能超过32 Kb。<li>-3: 每个quicklist节点上的ziplist大小不能超过16 Kb。<li>-2: 每个quicklist节点上的ziplist大小不能超过8 Kb。(-2是Redis给出的默认值)也就是上面的 <code>quicklist->fill = -2;</code><li>-1: 每个quicklist节点上的ziplist大小不能超过4 Kb。</ul><h2 id=压缩><a class=headerlink href=#压缩 title=压缩></a>压缩</h2><p><code>list-compress-depth</code>这个参数呢是用来配置压缩的,等等压缩是为啥,不是里面已经是压缩表了么,大牛们就是为了性能殚精竭虑,这里考虑到的是一个场景,一般状况下,list 都是两端的访问频率比较高,那么是不是可以对中间的数据进行压缩,那么这个参数就是用来表示<figure class="highlight plaintext"><table><tr><td class=gutter><pre><span class=line>1</span><br></pre><td class=code><pre><span class=line>/* depth of end nodes not to compress;0=off */</span><br></pre></table></figure><ul><li>0,代表不压缩,默认值<li>1,两端各一个节点不压缩<li>2,两端各两个节点不压缩<li>… 依次类推<br>压缩后的 ziplist 就会变成 quicklistLZF,然后替换 zl 指针,这里使用的是 <a href=http://oldhome.schmorp.de/marc/liblzf.html rel=noopener target=_blank>LZF</a> 压缩算法,压缩后的 quicklistLZF 中的 compressed 也是个柔性数组,压缩后的 ziplist 整个就放进这个柔性数组</ul><h2 id=插入过程><a class=headerlink href=#插入过程 title=插入过程></a>插入过程</h2><p>简单说下插入元素的过程<figure class="highlight plaintext"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br><span class=line>5</span><br><span class=line>6</span><br><span class=line>7</span><br><span class=line>8</span><br><span class=line>9</span><br><span class=line>10</span><br><span class=line>11</span><br><span class=line>12</span><br><span class=line>13</span><br><span class=line>14</span><br><span class=line>15</span><br><span class=line>16</span><br><span class=line>17</span><br><span class=line>18</span><br><span class=line>19</span><br><span class=line>20</span><br><span class=line>21</span><br><span class=line>22</span><br><span class=line>23</span><br><span class=line>24</span><br><span class=line>25</span><br><span class=line>26</span><br><span class=line>27</span><br><span class=line>28</span><br><span class=line>29</span><br><span class=line>30</span><br><span class=line>31</span><br><span class=line>32</span><br><span class=line>33</span><br><span class=line>34</span><br><span class=line>35</span><br><span class=line>36</span><br><span class=line>37</span><br><span class=line>38</span><br><span class=line>39</span><br><span class=line>40</span><br><span class=line>41</span><br><span class=line>42</span><br><span class=line>43</span><br><span class=line>44</span><br><span class=line>45</span><br><span class=line>46</span><br><span class=line>47</span><br><span class=line>48</span><br><span class=line>49</span><br><span class=line>50</span><br><span class=line>51</span><br><span class=line>52</span><br><span class=line>53</span><br><span class=line>54</span><br><span class=line>55</span><br><span class=line>56</span><br><span class=line>57</span><br><span class=line>58</span><br><span class=line>59</span><br><span class=line>60</span><br><span class=line>61</span><br><span class=line>62</span><br><span class=line>63</span><br><span class=line>64</span><br><span class=line>65</span><br><span class=line>66</span><br><span class=line>67</span><br><span class=line>68</span><br><span class=line>69</span><br><span class=line>70</span><br><span class=line>71</span><br><span class=line>72</span><br><span class=line>73</span><br><span class=line>74</span><br><span class=line>75</span><br><span class=line>76</span><br><span class=line>77</span><br><span class=line>78</span><br><span class=line>79</span><br><span class=line>80</span><br><span class=line>81</span><br><span class=line>82</span><br><span class=line>83</span><br><span class=line>84</span><br><span class=line>85</span><br><span class=line>86</span><br><span class=line>87</span><br><span class=line>88</span><br><span class=line>89</span><br><span class=line>90</span><br><span class=line>91</span><br><span class=line>92</span><br><span class=line>93</span><br><span class=line>94</span><br><span class=line>95</span><br><span class=line>96</span><br><span class=line>97</span><br><span class=line>98</span><br><span class=line>99</span><br><span class=line>100</span><br><span class=line>101</span><br><span class=line>102</span><br><span class=line>103</span><br><span class=line>104</span><br><span class=line>105</span><br><span class=line>106</span><br><span class=line>107</span><br></pre><td class=code><pre><span class=line>/* Wrapper to allow argument-based switching between HEAD/TAIL pop */</span><br><span class=line>void quicklistPush(quicklist *quicklist, void *value, const size_t sz,</span><br><span class=line> int where) {</span><br><span class=line> if (where == QUICKLIST_HEAD) {</span><br><span class=line> quicklistPushHead(quicklist, value, sz);</span><br><span class=line> } else if (where == QUICKLIST_TAIL) {</span><br><span class=line> quicklistPushTail(quicklist, value, sz);</span><br><span class=line> }</span><br><span class=line>}</span><br><span class=line></span><br><span class=line>/* Add new entry to head node of quicklist.</span><br><span class=line> *</span><br><span class=line> * Returns 0 if used existing head.</span><br><span class=line> * Returns 1 if new head created. */</span><br><span class=line>int quicklistPushHead(quicklist *quicklist, void *value, size_t sz) {</span><br><span class=line> quicklistNode *orig_head = quicklist->head;</span><br><span class=line> if (likely(</span><br><span class=line> _quicklistNodeAllowInsert(quicklist->head, quicklist->fill, sz))) {</span><br><span class=line> quicklist->head->zl =</span><br><span class=line> ziplistPush(quicklist->head->zl, value, sz, ZIPLIST_HEAD);</span><br><span class=line> quicklistNodeUpdateSz(quicklist->head);</span><br><span class=line> } else {</span><br><span class=line> quicklistNode *node = quicklistCreateNode();</span><br><span class=line> node->zl = ziplistPush(ziplistNew(), value, sz, ZIPLIST_HEAD);</span><br><span class=line></span><br><span class=line> quicklistNodeUpdateSz(node);</span><br><span class=line> _quicklistInsertNodeBefore(quicklist, quicklist->head, node);</span><br><span class=line> }</span><br><span class=line> quicklist->count++;</span><br><span class=line> quicklist->head->count++;</span><br><span class=line> return (orig_head != quicklist->head);</span><br><span class=line>}</span><br><span class=line></span><br><span class=line>/* Add new entry to tail node of quicklist.</span><br><span class=line> *</span><br><span class=line> * Returns 0 if used existing tail.</span><br><span class=line> * Returns 1 if new tail created. */</span><br><span class=line>int quicklistPushTail(quicklist *quicklist, void *value, size_t sz) {</span><br><span class=line> quicklistNode *orig_tail = quicklist->tail;</span><br><span class=line> if (likely(</span><br><span class=line> _quicklistNodeAllowInsert(quicklist->tail, quicklist->fill, sz))) {</span><br><span class=line> quicklist->tail->zl =</span><br><span class=line> ziplistPush(quicklist->tail->zl, value, sz, ZIPLIST_TAIL);</span><br><span class=line> quicklistNodeUpdateSz(quicklist->tail);</span><br><span class=line> } else {</span><br><span class=line> quicklistNode *node = quicklistCreateNode();</span><br><span class=line> node->zl = ziplistPush(ziplistNew(), value, sz, ZIPLIST_TAIL);</span><br><span class=line></span><br><span class=line> quicklistNodeUpdateSz(node);</span><br><span class=line> _quicklistInsertNodeAfter(quicklist, quicklist->tail, node);</span><br><span class=line> }</span><br><span class=line> quicklist->count++;</span><br><span class=line> quicklist->tail->count++;</span><br><span class=line> return (orig_tail != quicklist->tail);</span><br><span class=line>}</span><br><span class=line></span><br><span class=line>/* Wrappers for node inserting around existing node. */</span><br><span class=line>REDIS_STATIC void _quicklistInsertNodeBefore(quicklist *quicklist,</span><br><span class=line> quicklistNode *old_node,</span><br><span class=line> quicklistNode *new_node) {</span><br><span class=line> __quicklistInsertNode(quicklist, old_node, new_node, 0);</span><br><span class=line>}</span><br><span class=line></span><br><span class=line>REDIS_STATIC void _quicklistInsertNodeAfter(quicklist *quicklist,</span><br><span class=line> quicklistNode *old_node,</span><br><span class=line> quicklistNode *new_node) {</span><br><span class=line> __quicklistInsertNode(quicklist, old_node, new_node, 1);</span><br><span class=line>}</span><br><span class=line></span><br><span class=line>/* Insert 'new_node' after 'old_node' if 'after' is 1.</span><br><span class=line> * Insert 'new_node' before 'old_node' if 'after' is 0.</span><br><span class=line> * Note: 'new_node' is *always* uncompressed, so if we assign it to</span><br><span class=line> * head or tail, we do not need to uncompress it. */</span><br><span class=line>REDIS_STATIC void __quicklistInsertNode(quicklist *quicklist,</span><br><span class=line> quicklistNode *old_node,</span><br><span class=line> quicklistNode *new_node, int after) {</span><br><span class=line> if (after) {</span><br><span class=line> new_node->prev = old_node;</span><br><span class=line> if (old_node) {</span><br><span class=line> new_node->next = old_node->next;</span><br><span class=line> if (old_node->next)</span><br><span class=line> old_node->next->prev = new_node;</span><br><span class=line> old_node->next = new_node;</span><br><span class=line> }</span><br><span class=line> if (quicklist->tail == old_node)</span><br><span class=line> quicklist->tail = new_node;</span><br><span class=line> } else {</span><br><span class=line> new_node->next = old_node;</span><br><span class=line> if (old_node) {</span><br><span class=line> new_node->prev = old_node->prev;</span><br><span class=line> if (old_node->prev)</span><br><span class=line> old_node->prev->next = new_node;</span><br><span class=line> old_node->prev = new_node;</span><br><span class=line> }</span><br><span class=line> if (quicklist->head == old_node)</span><br><span class=line> quicklist->head = new_node;</span><br><span class=line> }</span><br><span class=line> /* If this insert creates the only element so far, initialize head/tail. */</span><br><span class=line> if (quicklist->len == 0) {</span><br><span class=line> quicklist->head = quicklist->tail = new_node;</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> if (old_node)</span><br><span class=line> quicklistCompress(quicklist, old_node);</span><br><span class=line></span><br><span class=line> quicklist->len++;</span><br><span class=line>}</span><br></pre></table></figure><p>前面第一步先根据插入的是头还是尾选择不同的 push 函数,quicklistPushHead 或者 quicklistPushTail,举例分析下从头插入的 quicklistPushHead,先判断当前的 quicklistNode 节点还能不能允许再往 ziplist 里添加元素,如果可以就添加,如果不允许就新建一个 quicklistNode,然后调用 _quicklistInsertNodeBefore 将节点插进去,具体插入quicklist节点的操作类似链表的插入。</div><footer class=post-footer><div class="affiliate-creative affiliate-creative--post-end" data-affiliate-id=tencent-cloud-general><a rel="sponsored noopener" aria-label=腾讯云产品优惠 href=https://cloud.tencent.com/act/cps/redirect?redirect=2446&cps_key=2e33a1eedb380997d03618b4a5ba6ca7&from=console target=_blank><img alt=腾讯云服务器、数据库和云产品优惠 decoding=async height=419 loading=lazy 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