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<a class="post-title-link" href="/2020/03/12/redis-sds-%E5%9C%A8dict-%E4%B8%AD%E7%9A%84%E4%B8%80%E7%82%B9%E5%A6%99%E7%94%A8/" itemprop="url">redis sds 在dict 中的一点妙用</a></h2>
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<li><p><a href="#0">redis 版本</a></p>
</li>
<li><p><a href="#0">sds 的一点妙用</a></p>
<hr>
<h3 id="0">redis 版本</h3>
<p> redis5.0 stable</p>
<h3 id="1">sds 的一点妙用</h3>
我们都知道.在redis 中,key 是被保存为sds 结构的，而不是普通的字符串。
相比较于传统的c的字符串，sds 主要是改进了2点。
<ul>
<li>有len 字段，将字符串的长度计算从o(n)变成了o(1)</li>
<li>减少修改字符串时带来的内存重分配次数</li>
</ul>
<p>今天我们来看看sds 在redis的作者是怎么利用这个len 字段来尽可能的优化redis 的速度的</p>
<p><code>SADD runset redis</code></p>
<p>在执行上面这个常见的redis 的命令的时候，redis 内部的第一项步骤其实就是查找 redis 这个value 是否已经存在于 runset 之中了。原因很简单<br><code>set 这个数据结构中是不允许存在两个相同的值的</code></p>
<p>那么redis 的作者是怎么实现这个功能的呢？</p>
<p>在我还是学生时代学c 的时候，我肯定是无脑上memcmp 的<br>redis 作者最终也是用到了这个函数,但是在用这个函数比较之前，有两个小小的判断</p>
<p> 判断两个sds 的起始内存地址是否相等。<br> key==he->key</p>
<hr>
<p> 如果上面的key != he->key,则执行dictSdsKeyCompare函数。<br> int dictSdsKeyCompare(void *privdata, const void *key1,</p>
<pre><code>const void *key2)</code></pre><p> {</p>
<pre><code>int l1,l2;
DICT_NOTUSED(privdata);
// sdslen 就是返回sds 的长度值
l1 = sdslen((sds)key1);
l2 = sdslen((sds)key2);
if (l1 != l2) return 0;
return memcmp(key1, key2, l1) == 0;</code></pre><p> }</p>
<p>redis 的作者为了一点点的运行速度真是拼了命的进行优化了</p>
</li>
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<h2 id="参考"><a href="#参考" class="headerlink" title="参考"></a>参考</h2><div id="refer-anchor-1"></div>
<ul>
<li>[1] <a href="https://zhuanlan.zhihu.com/p/51075839" target="_blank" rel="noopener">redis sds</a></li>
<li>[2] <a href="http://cbsheng.github.io/posts/redis%E6%BA%90%E7%A0%81%E5%88%86%E6%9E%90%E4%B9%8Bsds%E5%AF%B9%E8%B1%A1/" target="_blank" rel="noopener">redis源码分析之sds对象</a></li>
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<ul>
<li><a href="#0">redis 版本</a></li>
<li><a href="#1">redis object 数据结构</a></li>
<li><a href="#2">robj -type</a></li>
<li><a href="#3">robj -encoding</a></li>
<li><a href="#4">robj -lru</a></li>
<li><a href="#5">robj -refcount</a></li>
<li><a href="#6">robj -ptr</a></li>
</ul>
<hr>
<h3 id="0">redis 版本</h3>
<pre><code>redis5.0 stable</code></pre> <h3 id="1">redis object 数据结构</h3>
遍观整个redis 源码,我常常能看到有下面的一个类型的定义
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">robj *subject;</span><br></pre></td></tr></table></figure>
<p>出于兴趣，我认真的研究了一下这个数据结构</p>
<p>首先是robj 的数据结构的定义</p>
<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></pre></td><td class="code"><pre><span class="line"><span class="keyword">typedef</span> <span class="class"><span class="keyword">struct</span> <span class="title">redisObject</span> {</span></span><br><span class="line"> <span class="keyword">unsigned</span> type:<span class="number">4</span>;</span><br><span class="line"> <span class="keyword">unsigned</span> encoding:<span class="number">4</span>;</span><br><span class="line"> <span class="keyword">unsigned</span> lru:LRU_BITS; <span class="comment">/* LRU time (relative to global lru_clock) or</span></span><br><span class="line"><span class="comment"> * LFU data (least significant 8 bits frequency</span></span><br><span class="line"><span class="comment"> * and most significant 16 bits access time). */</span></span><br><span class="line"> <span class="keyword">int</span> refcount;</span><br><span class="line"> <span class="keyword">void</span> *ptr;</span><br><span class="line">} robj;</span><br></pre></td></tr></table></figure>
<p>可以看到robj 的字段并不多。<br>下面我们来一一讲解这些字段</p>
<h3 id="2">redis type</h3>
type 主要是用来指代ptr 的数据类型。
下面是redis 中定义的几种Type 类型的值
<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></pre></td><td class="code"><pre><span class="line"><span class="meta">#<span class="meta-keyword">define</span> OBJ_STRING 0 <span class="comment">/* String object. */</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">define</span> OBJ_LIST 1 <span class="comment">/* List object. */</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">define</span> OBJ_SET 2 <span class="comment">/* Set object. */</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">define</span> OBJ_ZSET 3 <span class="comment">/* Sorted set object. */</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">define</span> OBJ_HASH 4 <span class="comment">/* Hash object. */</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">define</span> OBJ_MODULE 5 <span class="comment">/* Module object. */</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">define</span> OBJ_STREAM 6 <span class="comment">/* Stream object. */</span></span></span><br></pre></td></tr></table></figure>
<h3 id="3">redis encoding</h3>
类型实现的编码方式
在redis 中 一个数据结构是有多重不同的编码的,
比如list 就有压缩列表实现的对象和双端列表实现的对象
<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></pre></td><td class="code"><pre><span class="line"><span class="meta">#<span class="meta-keyword">define</span> OBJ_ENCODING_RAW 0 <span class="comment">/* Raw representation */</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">define</span> OBJ_ENCODING_INT 1 <span class="comment">/* Encoded as integer */</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">define</span> OBJ_ENCODING_HT 2 <span class="comment">/* Encoded as hash table */</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">define</span> OBJ_ENCODING_ZIPMAP 3 <span class="comment">/* Encoded as zipmap */</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">define</span> OBJ_ENCODING_LINKEDLIST 4 <span class="comment">/* No longer used: old list encoding. */</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">define</span> OBJ_ENCODING_ZIPLIST 5 <span class="comment">/* Encoded as ziplist */</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">define</span> OBJ_ENCODING_INTSET 6 <span class="comment">/* Encoded as intset */</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">define</span> OBJ_ENCODING_SKIPLIST 7 <span class="comment">/* Encoded as skiplist */</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">define</span> OBJ_ENCODING_EMBSTR 8 <span class="comment">/* Embedded sds string encoding */</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">define</span> OBJ_ENCODING_QUICKLIST 9 <span class="comment">/* Encoded as linked list of ziplists */</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">define</span> OBJ_ENCODING_STREAM 10 <span class="comment">/* Encoded as a radix tree of listpacks */</span></span></span><br></pre></td></tr></table></figure>
<h3 id="4">redis lru</h3>
熟悉操作系统的人应该都知道一个lru 算法。
这个就是和那个类似。主要在当内存资源有限的情况下,淘汰长期不用的数据。
<h3 id="5">redis refcount</h3>
对象的引用计数,用于垃圾回收
<h3 id="6">redis ptr</h3>
真正的数据，可以是set，list等
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<a class="post-title-link" href="/2020/03/11/insert-command-%E6%B5%81%E7%A8%8B%E6%8E%A2%E7%A9%B6/" itemprop="url">insert command 流程探究</a></h2>
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<ul>
<li><p><a href="#0">要探究的command</a></p>
</li>
<li><p><a href="#1">redis 版本</a></p>
</li>
<li><p><a href="#2">insert command 调用堆栈</a></p>
</li>
<li><p><a href="#3">inster command 流程图</a></p>
</li>
<li><p><a href="#4">client 数据结构</a></p>
</li>
<li><p><a href="#5">insert command code</a></p>
<h3 id="0">要探究的command</h3>
<p> LINSERT run before “redis” “redis1”</p>
<h3 id="1">redis 版本</h3>
<p> redis5.0 stable</p>
<h3 id="2">insert command 调用堆栈</h3>
</li>
</ul>
<ul>
<li>linsertCommand (src/t_list.c:269)<br></li>
<li>call (src/server.c:2468)<br></li>
<li>processCommand (src/server.c:2763)<br></li>
<li>processInputBuffer (src/networking.c:1466)<br></li>
<li>processInputBufferAndReplicate (src/networking.c:1501)<br></li>
<li>readQueryFromClient (src/networking.c:1583)<br></li>
<li>aeProcessEvents (src/ae.c:443)<br></li>
<li>aeMain (src/ae.c:501)<br></li>
<li>main (src/server.c:4235)<br></li>
</ul>
<h3 id="3">inster command 流程图</h3>
<p> <img src="https://upload-images.jianshu.io/upload_images/1250148-c97df494e2dc7bc3.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240" alt="Untitled Diagram.png"></p>
<h3 id="4">client 数据结构</h3>
这里只介绍几个和我们执行这几个命令比较相关的字段
<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><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></pre></td><td class="code"><pre><span class="line"><span class="keyword">typedef</span> <span class="class"><span class="keyword">struct</span> <span class="title">client</span> {</span></span><br><span class="line"> <span class="keyword">uint64_t</span> id; <span class="comment">/* Client incremental unique ID. */</span></span><br><span class="line"> <span class="keyword">int</span> fd; <span class="comment">//文件描述符,主要是将返回的结果返回给界面 /* Client socket. </span></span><br><span class="line"> redisDb *db; <span class="comment">/* Pointer to currently SELECTed DB. */</span></span><br><span class="line"> robj *name; <span class="comment">/* As set by CLIENT SETNAME. */</span></span><br><span class="line"> sds querybuf; <span class="comment">/* Buffer we use to accumulate client queries. */</span></span><br><span class="line"> <span class="keyword">size_t</span> qb_pos; <span class="comment">/* The position we have read in querybuf. */</span></span><br><span class="line"> sds pending_querybuf; <span class="comment">/* If this client is flagged as master, this buffer</span></span><br><span class="line"><span class="comment"> represents the yet not applied portion of the</span></span><br><span class="line"><span class="comment"> replication stream that we are receiving from</span></span><br><span class="line"><span class="comment"> the master. */</span></span><br><span class="line"> <span class="keyword">size_t</span> querybuf_peak; <span class="comment">/* Recent (100ms or more) peak of querybuf size. */</span></span><br><span class="line"> <span class="keyword">int</span> argc; <span class="comment">/* Num of arguments of current command. */</span></span><br><span class="line"> robj **argv; <span class="comment">/* Arguments of current command. */</span></span><br><span class="line"> <span class="class"><span class="keyword">struct</span> <span class="title">redisCommand</span> *<span class="title">cmd</span>, *<span class="title">lastcmd</span>;</span> <span class="comment">/* Last command executed. */</span></span><br><span class="line"> <span class="keyword">int</span> reqtype; <span class="comment">/* Request protocol type: PROTO_REQ_* */</span></span><br><span class="line"> <span class="keyword">int</span> multibulklen; <span class="comment">/* Number of multi bulk arguments left to read. */</span></span><br><span class="line"> <span class="keyword">long</span> bulklen; <span class="comment">/* Length of bulk argument in multi bulk request. */</span></span><br><span class="line"> <span class="built_in">list</span> *reply; <span class="comment">/* List of reply objects to send to the client. */</span></span><br><span class="line"> <span class="keyword">unsigned</span> <span class="keyword">long</span> <span class="keyword">long</span> reply_bytes; <span class="comment">/* Tot bytes of objects in reply list. */</span></span><br><span class="line"> <span class="keyword">size_t</span> sentlen; <span class="comment">/* Amount of bytes already sent in the current</span></span><br><span class="line"><span class="comment"> buffer or object being sent. */</span></span><br><span class="line"> <span class="keyword">time_t</span> ctime; <span class="comment">/* Client creation time. */</span></span><br><span class="line"> <span class="keyword">time_t</span> lastinteraction; <span class="comment">/* Time of the last interaction, used for timeout */</span></span><br><span class="line"> <span class="keyword">time_t</span> obuf_soft_limit_reached_time;</span><br><span class="line"> <span class="keyword">int</span> flags; <span class="comment">/* Client flags: CLIENT_* macros. */</span></span><br><span class="line"> <span class="keyword">int</span> authenticated; <span class="comment">/* When requirepass is non-NULL. */</span></span><br><span class="line"> <span class="keyword">int</span> replstate; <span class="comment">/* Replication state if this is a slave. */</span></span><br><span class="line"> <span class="keyword">int</span> repl_put_online_on_ack; <span class="comment">/* Install slave write handler on first ACK. */</span></span><br><span class="line"> <span class="keyword">int</span> repldbfd; <span class="comment">/* Replication DB file descriptor. */</span></span><br><span class="line"> <span class="keyword">off_t</span> repldboff; <span class="comment">/* Replication DB file offset. */</span></span><br><span class="line"> <span class="keyword">off_t</span> repldbsize; <span class="comment">/* Replication DB file size. */</span></span><br><span class="line"> sds replpreamble; <span class="comment">/* Replication DB preamble. */</span></span><br><span class="line"> <span class="keyword">long</span> <span class="keyword">long</span> read_reploff; <span class="comment">/* Read replication offset if this is a master. */</span></span><br><span class="line"> <span class="keyword">long</span> <span class="keyword">long</span> reploff; <span class="comment">/* Applied replication offset if this is a master. */</span></span><br><span class="line"> <span class="keyword">long</span> <span class="keyword">long</span> repl_ack_off; <span class="comment">/* Replication ack offset, if this is a slave. */</span></span><br><span class="line"> <span class="keyword">long</span> <span class="keyword">long</span> repl_ack_time;<span class="comment">/* Replication ack time, if this is a slave. */</span></span><br><span class="line"> <span class="keyword">long</span> <span class="keyword">long</span> psync_initial_offset; <span class="comment">/* FULLRESYNC reply offset other slaves</span></span><br><span class="line"><span class="comment"> copying this slave output buffer</span></span><br><span class="line"><span class="comment"> should use. */</span></span><br><span class="line"> <span class="keyword">char</span> replid[CONFIG_RUN_ID_SIZE+<span class="number">1</span>]; <span class="comment">/* Master replication ID (if master). */</span></span><br><span class="line"> <span class="keyword">int</span> slave_listening_port; <span class="comment">/* As configured with: SLAVECONF listening-port */</span></span><br><span class="line"> <span class="keyword">char</span> slave_ip[NET_IP_STR_LEN]; <span class="comment">/* Optionally given by REPLCONF ip-address */</span></span><br><span class="line"> <span class="keyword">int</span> slave_capa; <span class="comment">/* Slave capabilities: SLAVE_CAPA_* bitwise OR. */</span></span><br><span class="line"> multiState mstate; <span class="comment">/* MULTI/EXEC state */</span></span><br><span class="line"> <span class="keyword">int</span> btype; <span class="comment">/* Type of blocking op if CLIENT_BLOCKED. */</span></span><br><span class="line"> blockingState bpop; <span class="comment">/* blocking state */</span></span><br><span class="line"> <span class="keyword">long</span> <span class="keyword">long</span> woff; <span class="comment">/* Last write global replication offset. */</span></span><br><span class="line"> <span class="built_in">list</span> *watched_keys; <span class="comment">/* Keys WATCHED for MULTI/EXEC CAS */</span></span><br><span class="line"> dict *pubsub_channels; <span class="comment">/* channels a client is interested in (SUBSCRIBE) */</span></span><br><span class="line"> <span class="built_in">list</span> *pubsub_patterns; <span class="comment">/* patterns a client is interested in (SUBSCRIBE) */</span></span><br><span class="line"> sds peerid; <span class="comment">/* Cached peer ID. */</span></span><br><span class="line"> listNode *client_list_node; <span class="comment">/* list node in client list */</span></span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Response buffer */</span></span><br><span class="line"> <span class="keyword">int</span> bufpos;</span><br><span class="line"> <span class="comment">// 返回的结果最终会写在buf数组里</span></span><br><span class="line"> <span class="keyword">char</span> buf[PROTO_REPLY_CHUNK_BYTES];</span><br><span class="line">} client;</span><br></pre></td></tr></table></figure>
<h3 id="5">insert command code</h3>
下面是执行这个command
<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><td class="code"><pre><span class="line"><span class="function"><span class="keyword">void</span> <span class="title">linsertCommand</span><span class="params">(client *c)</span> </span>{</span><br><span class="line"> <span class="keyword">int</span> where;</span><br><span class="line"> robj *subject;</span><br><span class="line"> listTypeIterator *iter;</span><br><span class="line"> listTypeEntry entry;</span><br><span class="line"> <span class="keyword">int</span> inserted = <span class="number">0</span>;</span><br><span class="line"> <span class="comment">// 这里主要是解析参数</span></span><br><span class="line"> <span class="keyword">if</span> (strcasecmp(c->argv[<span class="number">2</span>]->ptr,<span class="string">"after"</span>) == <span class="number">0</span>) {</span><br><span class="line"> where = LIST_TAIL;</span><br><span class="line"> } <span class="keyword">else</span> <span class="keyword">if</span> (strcasecmp(c->argv[<span class="number">2</span>]->ptr,<span class="string">"before"</span>) == <span class="number">0</span>) {</span><br><span class="line"> where = LIST_HEAD;</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> addReply(c,shared.syntaxerr);</span><br><span class="line"> <span class="keyword">return</span>;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> ((subject = lookupKeyWriteOrReply(c,c->argv[<span class="number">1</span>],shared.czero)) == <span class="literal">NULL</span> ||</span><br><span class="line"> checkType(c,subject,OBJ_LIST)) <span class="keyword">return</span>;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Seek pivot from head to tail */</span></span><br><span class="line"> <span class="comment">// 从这里可以看出来这个是查找就是从头查找到尾的,时间复杂度为o(N)</span></span><br><span class="line"> iter = listTypeInitIterator(subject,<span class="number">0</span>,LIST_TAIL);</span><br><span class="line"> <span class="keyword">while</span> (listTypeNext(iter,&entry)) {</span><br><span class="line"> <span class="keyword">if</span> (listTypeEqual(&entry,c->argv[<span class="number">3</span>])) {</span><br><span class="line"> listTypeInsert(&entry,c->argv[<span class="number">4</span>],where);</span><br><span class="line"> inserted = <span class="number">1</span>;</span><br><span class="line"> <span class="keyword">break</span>;</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"> <span class="comment">// 获取链表的迭代器</span></span><br><span class="line"> listTypeReleaseIterator(iter);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (inserted) {</span><br><span class="line"> signalModifiedKey(c->db,c->argv[<span class="number">1</span>]);</span><br><span class="line"> notifyKeyspaceEvent(NOTIFY_LIST,<span class="string">"linsert"</span>,</span><br><span class="line"> c->argv[<span class="number">1</span>],c->db->id);</span><br><span class="line"> server.dirty++;</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> <span class="comment">/* Notify client of a failed insert */</span></span><br><span class="line"> addReply(c,shared.cnegone);</span><br><span class="line"> <span class="keyword">return</span>;</span><br><span class="line"> }</span><br><span class="line"> <span class="comment">// 这里是将插入后的结果写入到c->buf中</span></span><br><span class="line"> addReplyLongLong(c,listTypeLength(subject));</span><br><span class="line"> }</span><br></pre></td></tr></table></figure>
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<a class="post-title-link" href="/2020/03/07/%E6%96%87%E4%BB%B6%E5%90%88%E5%B9%B6/" itemprop="url">文件合并</a></h2>
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<p>最近碰到如下的一个问题 如何快速合并两个大文件？</p>
<p>有A,B两个文件。这两个文件都有以下特性</p>
<ol>
<li><p>A,B两个文件每一行都可以被解析为json 格式</p>
</li>
<li><p>A,B两个文件都比较大(至少大于500M)</p>
</li>
<li><p>A,B两个文件可以通过将每行转化为json之后通过某个相同key的值合并</p>
</li>
<li><p>A文件有a行,B文件有b行</p>
</li>
<li><p>A,B两个文件两行可以合并的条件是唯一的。</p>
<blockquote>
<p>比如 A文件的第一行可以是这样的一个json </p>
<p>{</p>
<p> ‘id’:1,</p>
<p> ‘test’: 2</p>
<p>}</p>
<p>B文件的第二行可以是这样的一个json</p>
<p>{</p>
<p> ‘id’:1,</p>
<p> ‘test2’:3</p>
<p>}</p>
<p>我们可以通过两个相同的key合并为这样一个json</p>
<p>{</p>
<p> ‘id’:1,</p>
<p> ‘test’:2,</p>
<p> ‘test2’:3</p>
<p>}</p>
</blockquote>
</li>
</ol>
<p>现在的问题就是如何把他们合并？</p>
<p>第一个想法——暴力合并</p>
<ol>
<li>先读取A文件的一行数据，然后转化为json格式</li>
<li>将A某一行的json格式的数据同B文件中的数据一一校验，判断两个数据数据是否可以合并</li>
</ol>
<p> </p>
<p>这个想法的算法复杂度是o(a*b)，当文件的行数很大的时候，情况很堪忧。以我目前的处理的两个文件来说，两个文件都是9万多行。对于cpu来说，他最坏的时候需要90000 * 90000次指令。目前的cpu每秒大概能执行百万级的指令，那么执行这个合并操作也需要2个小时的时间</p>
<p>第二个方法-先预处理一下</p>
<p>我们可以先算出A文件中哪一行数据可以同B文件中哪几行的文件。因为合并的条件是唯一的。那么对于我们现在的处理的文件来说是算法复杂度为o(max(a,b))</p>
<p>但是这个算法还是有一个问题，当你已经知道两个文件哪俩行的文件需要合并的。你如何从这两个大文件中快速的读出这两行文件。</p>
<p>我目前的想法是记录每一行的偏移量的位置。</p>
<p>记录偏移量的话我刚开始是想采用以下代码的方法的。直接把文件中的数据读到内存中</p>
<p>执行以下代码,276M 需要2秒,17G 需要10秒</p>
<figure class="highlight python"><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></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">def</span> <span class="title">test_merge</span><span class="params">(filename)</span>:</span></span><br><span class="line"> start_time = time.time()</span><br><span class="line"> <span class="keyword">print</span> <span class="string">"start {} function is {}"</span>.format(test_merge.__name__, start_time)</span><br><span class="line"> </span><br><span class="line"> f = open(filename, <span class="string">"r"</span>)</span><br><span class="line"> line = []</span><br><span class="line"> line.append(<span class="number">0</span>)</span><br><span class="line"> filename_size = os.path.getsize(filename)</span><br><span class="line"> chars = f.read(filename_size)</span><br><span class="line"> count = <span class="number">0</span></span><br><span class="line"> <span class="keyword">for</span> char <span class="keyword">in</span> chars:</span><br><span class="line"> <span class="keyword">if</span> char == <span class="string">'\n'</span>:</span><br><span class="line"> line.append(count)</span><br><span class="line"> count = count + <span class="number">1</span></span><br></pre></td></tr></table></figure>
<p>但是上面的代码在当文件很大的时候是很容易爆内存的.</p>
<p>所以在此我们可以采用第二个函数可以通过，先计算出每个文件的大小，然后每个读出根号大小的数</p>
<figure class="highlight python"><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></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">def</span> <span class="title">merge_by_file</span><span class="params">(filename)</span>:</span></span><br><span class="line"> start_time = time.time()</span><br><span class="line"> <span class="keyword">print</span> <span class="string">"start {} function is {}"</span>.format(merge_by_file.__name__,start_time)</span><br><span class="line"> </span><br><span class="line"> f = open(filename, <span class="string">"r"</span>)</span><br><span class="line"> line = []</span><br><span class="line"> line.append(<span class="number">0</span>)</span><br><span class="line"> filename_size = os.path.getsize(filename)</span><br><span class="line"> filename_length = int(math.sqrt(filename_size))</span><br><span class="line"> count = <span class="number">0</span></span><br><span class="line"> <span class="keyword">print</span> filename_length</span><br><span class="line"> <span class="keyword">for</span> i <span class="keyword">in</span> xrange(filename_length + <span class="number">2</span>):</span><br><span class="line"> <span class="keyword">if</span> count + filename_length < filename_size:</span><br><span class="line"> chars = f.read(filename_length)</span><br><span class="line"> <span class="keyword">for</span> char <span class="keyword">in</span> chars:</span><br><span class="line"> count = count + <span class="number">1</span></span><br><span class="line"> <span class="keyword">if</span> char == <span class="string">'\n'</span>:</span><br><span class="line"> line.append(count)</span><br><span class="line"> <span class="keyword">else</span>:</span><br><span class="line"> chars = f.read(filename_size - count)</span><br><span class="line"> <span class="keyword">for</span> char <span class="keyword">in</span> chars:</span><br><span class="line"> count = count + <span class="number">1</span></span><br><span class="line"> <span class="keyword">if</span> char == <span class="string">'\n'</span> <span class="keyword">and</span> count != filename_size:</span><br><span class="line"> line.append(count)</span><br><span class="line"> <span class="keyword">break</span></span><br><span class="line"> f.close()</span><br></pre></td></tr></table></figure>
<p>由此，我在处理两个9万行文件的脚本每次运行的时间缩短到2分钟。</p>
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<pre><code>记探寻python 中int 函数中的一点小曲折</code></pre><p> 今天在复习python 源码的时候.突然发现了一个奇怪的结果.代码如下</p>
<figure class="highlight python"><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></pre></td><td class="code"><pre><span class="line">In [<span class="number">2</span>]: a = <span class="number">11111111111111111111111111</span></span><br><span class="line"></span><br><span class="line">In [<span class="number">3</span>]: a = (int)(a)</span><br><span class="line"></span><br><span class="line">In [<span class="number">4</span>]: type(a)</span><br><span class="line">Out[<span class="number">4</span>]: long</span><br><span class="line"></span><br><span class="line">In [<span class="number">5</span>]: a = int(a)</span><br><span class="line"></span><br><span class="line">In [<span class="number">6</span>]: type(a)</span><br><span class="line">Out[<span class="number">6</span>]: long</span><br></pre></td></tr></table></figure>
<p>这个结果让我有点吃惊，刚开始我是以为是python 的强制类型转换的问题.因为在我之前的意识中一直觉的int 这个函数是类似于c中的强制类型转换。</p>
<p>接着我开始看了下这个函数的文档。粗略的看了下没发现啥有用的。接着在谷歌上搜寻答案,用了python 强制类型转换和 python 强制类型转换 源码 。。。等几个关键字，都没发现啥有营养的结果。</p>
<p>在搜索无果的情况下。只得求助stackoverflow 社区。幸得别人指点又跑回去重新看了下文档。发现文档在在中间其实写了这么一段 </p>
<p>If the argument is outside the integer range, the function returns a long object instead.</p>
<p>。。。 默默无语。</p>
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