某企业级hadoop源代码分析-1

本文尝试分析某大型大数据解决方案公司企业级hadoop源代码，班门弄斧。
本系列将分三篇文章，对所做的修改进行分析。

修改点1

Index: org/apache/hadoop/hdfs/server/namenode/AclTransformation.java===================================================================--- org/apache/hadoop/hdfs/server/namenode/AclTransformation.java   (revision 37)+++ org/apache/hadoop/hdfs/server/namenode/AclTransformation.java   (revision 42)@@ -62,7 +62,7 @@  */ @InterfaceAudience.Private final class AclTransformation {-  private static final int MAX_ENTRIES = 32;+  private static final int MAX_ENTRIES = 64;

分析

其中AclTransformation是acl操作类，MAX_ENTRIES表示所能存储的最大acl条目数。该条修改能够增加存储条目，无法在性能方面有所作为。

1.MAX_ENTRIES相关的源码。

  /**   * Builds the final list of ACL entries to return by trimming, sorting and   * validating the ACL entries that have been added.   *   * @param aclBuilder ArrayList<AclEntry> containing entries to build   * @return List<AclEntry> unmodifiable, sorted list of ACL entries   * @throws AclException if validation fails   */  private static List<AclEntry> buildAndValidateAcl(      ArrayList<AclEntry> aclBuilder) throws AclException {    if (aclBuilder.size() > MAX_ENTRIES) {      throw new AclException("Invalid ACL: ACL has " + aclBuilder.size() +        " entries, which exceeds maximum of " + MAX_ENTRIES + ".");    }

2.AclTransformation类注释及简单翻译

/** * AclTransformation defines the operations that can modify an ACL.  All ACL * modifications take as input an existing ACL and apply logic to add new * entries, modify existing entries or remove old entries.  Some operations also * accept an ACL spec: a list of entries that further describes the requested * change.  Different operations interpret the ACL spec differently.  In the * case of adding an ACL to an inode that previously did not have one, the * existing ACL can be a "minimal ACL" containing exactly 3 entries for owner, * group and other, all derived from the {@link FsPermission} bits. * * The algorithms implemented here require sorted lists of ACL entries.  For any * existing ACL, it is assumed that the entries are sorted.  This is because all * ACL creation and modification is intended to go through these methods, and * they all guarantee correct sort order in their outputs.  However, an ACL spec * is considered untrusted user input, so all operations pre-sort the ACL spec as * the first step. */

AclTransformation定义了修改acl的操作。所有的acl修改都是通过新增一条acl实现，实现添加，修改，删除。
一些操作也接受acl列表作为参数，不同的操作对acl列表的处理也不一样。当给一个没有进行过授权操作的inode添加acl时，inode包含最小化的acl，即owner，group，other三条acl，这三条acl从FsPermission继承而来。

这里Acl入口列表是有序的。所有已存在的ACL，其入口都是排序的。
这么做是因为所有的acl创建和都要经过这些方法，他们都保证他们的输出是正确排序的。
然而ACL spec被默认为不被信任的用户输入，所有操作都会首先对Acl spec进行预排序。

3.保证排序的代码

  /**   * Comparator that enforces required ordering for entries within an ACL:   * -owner entry (unnamed user)   * -all named user entries (internal ordering undefined)   * -owning group entry (unnamed group)   * -all named group entries (internal ordering undefined)   * -mask entry   * -other entry   * All access ACL entries sort ahead of all default ACL entries.   */  static final Comparator<AclEntry> ACL_ENTRY_COMPARATOR =    new Comparator<AclEntry>() {      @Override      public int compare(AclEntry entry1, AclEntry entry2) {        return ComparisonChain.start()          .compare(entry1.getScope(), entry2.getScope(),            Ordering.explicit(ACCESS, DEFAULT))          .compare(entry1.getType(), entry2.getType(),            Ordering.explicit(USER, GROUP, MASK, OTHER))          .compare(entry1.getName(), entry2.getName(),            Ordering.natural().nullsFirst())          .result();      }    };