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Cassandra Readins
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<b>1.</b>
Cassandra启动
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<b>2.1.</b>
创建ColumnFamilyStore
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<b>2.3.</b>
Cassandra Cache
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<b>3.</b>
Cassandra写入过程
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<h1 id="cassandra-">Cassandra 启动</h1>
<h2 id="databasedescritor">DatabaseDescritor初始化</h2>
<p>读取cassandra.yaml配置文件, 存储到Config类， 从Config类中读取配置参数, 来初始化部分配置类</p>
<p>重点谈论下DatabaseDescriptor对SystemKeyspace的初始化, System Keyspace是写死在KSMetaData中</p>
<pre><code class="lang-java"><span class="hljs-function"><span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title">applyConfig</span><span class="hljs-params">(Config config)</span> <span class="hljs-keyword">throws</span> ConfigurationException</span>{
List<KSMetaData> systemKeyspaces = Arrays.asList(KSMetaData.systemKeyspace());
<span class="hljs-keyword">assert</span> systemKeyspaces.size() == Schema.systemKeyspaceNames.size();
<span class="hljs-keyword">for</span> (KSMetaData ksmd : systemKeyspaces)
<span class="hljs-comment">//将每个KSMetaData下面的CFMetaData的UUID存入cfIdMap, KSMetaData存入keyspaces</span>
Schema.instance.load(ksmd);
}
</code></pre>
<p>Schema类结构</p>
<pre><code class="lang-java">NonBlockingHashMap<String, KSMetaData> keyspaces; <span class="hljs-comment">//ksName --> KSMataData</span>
NonBlockingHashMap<String, Keyspace> keyspaceInstances; <span class="hljs-comment">//ksName --> Keyspace</span>
ConcurrentBiMap<Pair<String, String>, UUID> cfIdMap; <span class="hljs-comment">//Pair<ksName, cfName> --> cfId</span>
</code></pre>
<h2 id="load-keyspaces--udfs">Load keyspaces 和 UDFs</h2>
<p>所有的keyspaces存储在system.schema_keyspaces中,ColumnFamily都存储在system.schema_columnfamilies，UTMetaData存储在system.schema_usertypes, UDFs存储在system.schema_functions，在CassandraDaemon.setup中触发。</p>
<pre><code class="lang-java"><span class="hljs-function"><span class="hljs-keyword">void</span> <span class="hljs-title">setup</span><span class="hljs-params">()</span></span>{
DatabaseDescriptor.loadSchemas();
Functions.loadUDFFromSchema();
}
<span class="hljs-comment">//DatabaseDescriptor.loadSchemas</span>
<span class="hljs-comment">// load kSMetaData, 同时也初始化Keyspace, 存入Schema.keyspaceInstances</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title">loadSchemas</span><span class="hljs-params">()</span></span>{
Schema.instance.load(DefsTables.loadFromKeyspace());
Schema.instance.updateVersion();
}
</code></pre>
<p>DefsTables类中全是静态方法，在loadFromKeyspace中主要关注</p>
<ul>
<li><p>ColumnFamilyStore创建及查询，查询具体细节参考查询一章</p>
<p>由于创建ColumnFamilyStore是在Keyspace类中执行，需要先初始化Keyspace, 再对每个ColumnFamily创建相应的ColumnFamilyStore</p>
<p>Keyspace类结构</p>
<pre><code class="lang-java"><span class="hljs-comment">//包含当前节点的token/identifier. token将会在节点之间gossip传递, 还维持其他节点负载信息柱状统计图</span>
KSMetaData metadata;
OpOrder writeOrder;
ConcurrentHashMap<UUID, ColumnFamilyStore> columnFamilyStores; <span class="hljs-comment">//cfId --> ColumnFamilyStore</span>
AbstractReplicationStrategy replicationStrategy;
</code></pre>
<p>初始化</p>
<pre><code class="lang-java"><span class="hljs-function"><span class="hljs-keyword">private</span> <span class="hljs-title">Keyspace</span><span class="hljs-params">(String keyspaceName, <span class="hljs-keyword">boolean</span> loadSSTables)</span></span>{
metadata = Schema.instance.getKSMetaData(keyspaceName);<span class="hljs-comment">//从schema取出KSMetaData</span>
createReplicationStrategy(metadata);<span class="hljs-comment">//创建ReplicationStrategy</span>
<span class="hljs-keyword">this</span>.metric = <span class="hljs-keyword">new</span> KeyspaceMetrics(<span class="hljs-keyword">this</span>);
<span class="hljs-keyword">for</span> (CFMetaData cfm : <span class="hljs-keyword">new</span> ArrayList<CFMetaData>(metadata.cfMetaData().values()))
{
initCf(cfm.cfId, cfm.cfName, loadSSTables);
}
}
<span class="hljs-comment">//在initCF中创建ColumnFamilyStore</span>
columnFamilyStores.putIfAbsent(cfId, ColumnFamilyStore.createColumnFamilyStore(<span class="hljs-keyword">this</span>, cfName, loadSSTables));
<span class="hljs-comment">//在Keyspace.open中对RowCache初始化</span>
<span class="hljs-keyword">for</span> (ColumnFamilyStore cfs : keyspaceInstance.getColumnFamilyStores())
cfs.initRowCache();
</code></pre>
</li>
<li>对结果的组装</li>
</ul>
<pre><code class="lang-java"><span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> Collection<KSMetaData> <span class="hljs-title">loadFromKeyspace</span><span class="hljs-params">()</span></span>{
<span class="hljs-comment">//执行查询</span>
List<Row> serializedSchema = SystemKeyspace.serializedSchema(SystemKeyspace.SCHEMA_KEYSPACES_CF);
List<KSMetaData> keyspaces = <span class="hljs-keyword">new</span> ArrayList<>(serializedSchema.size());
<span class="hljs-keyword">for</span> (Row row : serializedSchema){
<span class="hljs-keyword">if</span> (Schema.invalidSchemaRow(row) || Schema.ignoredSchemaRow(row))
<span class="hljs-keyword">continue</span>;
<span class="hljs-comment">//还需要对ColumnFamily, UserType进行查询</span>
keyspaces.add(KSMetaData.fromSchema(row, serializedColumnFamilies(row.key), serializedUserTypes(row.key)));
}
<span class="hljs-keyword">return</span> keyspaces;
}
<span class="hljs-comment">//在KSMetaData中对Row执行反序列化</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> KSMetaData <span class="hljs-title">fromSchema</span><span class="hljs-params">(Row serializedKs, Row serializedCFs, Row serializedUserTypes)</span></span>{
Map<String, CFMetaData> cfs = deserializeColumnFamilies(serializedCFs);
UTMetaData userTypes = <span class="hljs-keyword">new</span> UTMetaData(UTMetaData.fromSchema(serializedUserTypes));
<span class="hljs-function"><span class="hljs-keyword">return</span> <span class="hljs-title">fromSchema</span><span class="hljs-params">(serializedKs, cfs.values()</span>, userTypes)</span>;
}
<span class="hljs-comment">//KSMataData结构</span>
String name;
Class<? extends AbstractReplicationStrategy> strategyClass;
Map<String, String> strategyOptions;
Map<String, CFMetaData> cfMetaData; <span class="hljs-comment">// cfName --> CFMetaData</span>
<span class="hljs-keyword">boolean</span> durableWrites; <span class="hljs-comment">//是否写入Commit log</span>
UTMetaData userTypes;
<span class="hljs-comment">//CFMetaData结构, 主要参数</span>
UUID cfId; <span class="hljs-comment">//内部id, 不会暴露给用户</span>
String ksName;
String cfName;
ColumnFamilyType cfType; <span class="hljs-comment">//standard or super</span>
CellNameType comparator; <span class="hljs-comment">// bytes, long, timeuuid, utf8, etc.</span>
</code></pre>
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