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Giovanni Matteo Fumarola updated HDFS-14102: -------------------------------------------- Summary: Performance improvement in BlockPlacementPolicyDefault (was: verifyBlockPlacement) > Performance improvement in BlockPlacementPolicyDefault > ------------------------------------------------------ > > Key: HDFS-14102 > URL: https://issues.apache.org/jira/browse/HDFS-14102 > Project: Hadoop HDFS > Issue Type: Improvement > Reporter: BELUGA BEHR > Assignee: BELUGA BEHR > Priority: Minor > Fix For: 3.3.0 > > Attachments: HDFS-14102.1.patch, HDFS-14102.2.patch, > HDFS-14102.3.patch > > > > {code:java|title=BlockPlacementPolicyDefault.java} > // 1. Check that all locations are different. > // 2. Count locations on different racks. > Set<String> racks = new TreeSet<>(); > for (DatanodeInfo dn : locs) > racks.add(dn.getNetworkLocation()); > ... > racks.size(){code} > > Here, the code is counting the number of distinct Network Locations. > However, it is using a TreeSet which has overhead to maintain item order and > uses a linked structure internally. This overhead is unneeded since all that > is required here is a count. > {quote}A NavigableSet implementation based on a TreeMap. The elements are > ordered using their natural ordering, or by a Comparator provided at set > creation time, depending on which constructor is used. > This implementation provides guaranteed log(n) time cost for the basic > operations (add, remove and contains). > [https://docs.oracle.com/javase/7/docs/api/java/util/TreeSet.html] > {quote} > > Use Java streams for readability and because it uses a {{HashSet}} under the > covers to perform the distinct action. {{HashSet}} uses an array internally > and has constant time performance for the {{add}} method. > [https://github.com/apache/hadoop/blob/27978bcb66a9130cbf26d37ec454c0b7fcdc2530/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlockPlacementPolicyDefault.java#L1042] -- This message was sent by Atlassian JIRA (v7.6.3#76005) --------------------------------------------------------------------- To unsubscribe, e-mail: hdfs-issues-unsubscr...@hadoop.apache.org For additional commands, e-mail: hdfs-issues-h...@hadoop.apache.org