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The following page has been changed by JeanDanielCryans: http://wiki.apache.org/hadoop/Hbase/Troubleshooting The comment on the change is: Added: Scanners keep getting timeouts ------------------------------------------------------------------------------ 1. [#7 Problem: DFS instability and/or regionserver lease timeouts] 1. [#8 Problem: Instability on Amazon EC2] 1. [#9 Problem: Zookeeper SessionExpired events] + 1. [#10 Problem: Scanners keep getting timeouts] [[Anchor(1)]] == 1. Problem: Master initializes, but Region Servers do not == @@ -158, +159 @@ }}} * For Java SE 6, some users have had success with {{{ -XX:+UseConcMarkSweepGC -XX:+CMSIncrementalMode -XX:ParallelGCThreads=8 }}} + [[Anchor(10)]] + == 10. Problem: Scanners keep getting timeouts == + * Client receives org.apache.hadoop.hbase.UnknownScannerException or timeouts even if the region server lease is really high. Fixed in HBase 0.20.0 + === Causes === + * The client, by default, fetches 30 rows when issuing the first next(). All the 29 other calls simply return rows from local memory. So if it takes 3 minutes to process a row and the timeout is set to 30 minutes, it is still not enough to cover 30 * 3 = 90 minutes. + === Resolution === + * Set hbase.client.scanner.caching in hbase-site.xml at a very low value like 1 or use HTable.setScannerCaching(1). +
