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Misha Dmitriev commented on HDFS-12051: --------------------------------------- Addressed Yongjun's comments and submitted a new patch. > Intern INOdeFileAttributes$SnapshotCopy.name byte[] arrays to save memory > ------------------------------------------------------------------------- > > Key: HDFS-12051 > URL: https://issues.apache.org/jira/browse/HDFS-12051 > Project: Hadoop HDFS > Issue Type: Improvement > Reporter: Misha Dmitriev > Assignee: Misha Dmitriev > Attachments: HDFS-12051.01.patch, HDFS-12051.02.patch, > HDFS-12051.03.patch, HDFS-12051.04.patch, HDFS-12051.05.patch, > HDFS-12051.06.patch > > > When snapshot diff operation is performed in a NameNode that manages several > million HDFS files/directories, NN needs a lot of memory. Analyzing one heap > dump with jxray (www.jxray.com), we observed that duplicate byte[] arrays > result in 6.5% memory overhead, and most of these arrays are referenced by > {{org.apache.hadoop.hdfs.server.namenode.INodeFileAttributes$SnapshotCopy.name}} > and {{org.apache.hadoop.hdfs.server.namenode.INodeFile.name}}: > {code} > 19. DUPLICATE PRIMITIVE ARRAYS > Types of duplicate objects: > Ovhd Num objs Num unique objs Class name > 3,220,272K (6.5%) 104749528 25760871 byte[] > .... > 1,841,485K (3.7%), 53194037 dup arrays (13158094 unique) > 3510556 of byte[17](112, 97, 114, 116, 45, 109, 45, 48, 48, 48, ...), 2228255 > of byte[8](48, 48, 48, 48, 48, 48, 95, 48), 357439 of byte[17](112, 97, 114, > 116, 45, 109, 45, 48, 48, 48, ...), 237395 of byte[8](48, 48, 48, 48, 48, 49, > 95, 48), 227853 of byte[17](112, 97, 114, 116, 45, 109, 45, 48, 48, 48, ...), > 179193 of byte[17](112, 97, 114, 116, 45, 109, 45, 48, 48, 48, ...), 169487 > of byte[8](48, 48, 48, 48, 48, 50, 95, 48), 145055 of byte[17](112, 97, 114, > 116, 45, 109, 45, 48, 48, 48, ...), 128134 of byte[8](48, 48, 48, 48, 48, 51, > 95, 48), 108265 of byte[17](112, 97, 114, 116, 45, 109, 45, 48, 48, 48, ...) > ... and 45902395 more arrays, of which 13158084 are unique > <-- > org.apache.hadoop.hdfs.server.namenode.INodeFileAttributes$SnapshotCopy.name > <-- org.apache.hadoop.hdfs.server.namenode.snapshot.FileDiff.snapshotINode > <-- {j.u.ArrayList} <-- > org.apache.hadoop.hdfs.server.namenode.snapshot.FileDiffList.diffs <-- > org.apache.hadoop.hdfs.server.namenode.snapshot.FileWithSnapshotFeature.diffs > <-- org.apache.hadoop.hdfs.server.namenode.INode$Feature[] <-- > org.apache.hadoop.hdfs.server.namenode.INodeFile.features <-- > org.apache.hadoop.hdfs.server.blockmanagement.BlockInfo.bc <-- ... (1 > elements) ... <-- > org.apache.hadoop.hdfs.server.blockmanagement.BlocksMap$1.entries <-- > org.apache.hadoop.hdfs.server.blockmanagement.BlocksMap.blocks <-- > org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.blocksMap <-- > org.apache.hadoop.hdfs.server.blockmanagement.BlockManager$BlockReportProcessingThread.this$0 > <-- j.l.Thread[] <-- j.l.ThreadGroup.threads <-- j.l.Thread.group <-- Java > Static: org.apache.hadoop.fs.FileSystem$Statistics.STATS_DATA_CLEANER > 409,830K (0.8%), 13482787 dup arrays (13260241 unique) > 430 of byte[32](116, 97, 115, 107, 95, 49, 52, 57, 55, 48, ...), 353 of > byte[32](116, 97, 115, 107, 95, 49, 52, 57, 55, 48, ...), 352 of > byte[32](116, 97, 115, 107, 95, 49, 52, 57, 55, 48, ...), 350 of > byte[32](116, 97, 115, 107, 95, 49, 52, 57, 55, 48, ...), 342 of > byte[32](116, 97, 115, 107, 95, 49, 52, 57, 55, 48, ...), 341 of > byte[32](116, 97, 115, 107, 95, 49, 52, 57, 55, 48, ...), 341 of > byte[32](116, 97, 115, 107, 95, 49, 52, 57, 55, 48, ...), 340 of > byte[32](116, 97, 115, 107, 95, 49, 52, 57, 55, 48, ...), 337 of > byte[32](116, 97, 115, 107, 95, 49, 52, 57, 55, 48, ...), 334 of > byte[32](116, 97, 115, 107, 95, 49, 52, 57, 55, 48, ...) > ... and 13479257 more arrays, of which 13260231 are unique > <-- org.apache.hadoop.hdfs.server.namenode.INodeFile.name <-- > org.apache.hadoop.hdfs.server.blockmanagement.BlockInfo.bc <-- > org.apache.hadoop.util.LightWeightGSet$LinkedElement[] <-- > org.apache.hadoop.hdfs.server.blockmanagement.BlocksMap$1.entries <-- > org.apache.hadoop.hdfs.server.blockmanagement.BlocksMap.blocks <-- > org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.blocksMap <-- > org.apache.hadoop.hdfs.server.blockmanagement.BlockManager$BlockReportProcessingThread.this$0 > <-- j.l.Thread[] <-- > org.apache.hadoop.hdfs.server.blockmanagement.BlocksMap$1.entries <-- > org.apache.hadoop.hdfs.server.blockmanagement.BlocksMap.blocks <-- > org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.blocksMap <-- > org.apache.hadoop.hdfs.server.blockmanagement.BlockManager$BlockReportProcessingThread.this$0 > <-- j.l.Thread[] <-- j.l.ThreadGroup.threads <-- j.l.Thread.group <-- Java > Static: org.apache.hadoop.fs.FileSystem$Statistics.STATS_DATA_CLEANER > .... > {code} > To eliminate this duplication and reclaim memory, we will need to write a > small class similar to StringInterner, but designed specifically for byte[] > arrays. -- This message was sent by Atlassian JIRA (v6.4.14#64029) --------------------------------------------------------------------- To unsubscribe, e-mail: hdfs-issues-unsubscr...@hadoop.apache.org For additional commands, e-mail: hdfs-issues-h...@hadoop.apache.org