[
https://issues.apache.org/jira/browse/HBASE-15236?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Appy updated HBASE-15236:
-------------------------
Status: Patch Available (was: Open)
> Inconsistent cell reads over multiple bulk-loaded HFiles
> --------------------------------------------------------
>
> Key: HBASE-15236
> URL: https://issues.apache.org/jira/browse/HBASE-15236
> Project: HBase
> Issue Type: Bug
> Reporter: Appy
> Assignee: Appy
> Attachments: HBASE-15236-master-v2.patch,
> HBASE-15236-master-v3.patch, HBASE-15236.patch, TestWithSingleHRegion.java,
> tables_data.zip
>
>
> If there are two bulkloaded hfiles in a region with same seqID, same
> timestamps and duplicate keys*, get and scan may return different values for
> a key. Not sure how this would happen, but one of our customer uploaded a
> dataset with 2 files in a single region and both having same bulk load
> timestamp. These files are small ~50M (I couldn't find any setting for max
> file size that could lead to 2 files). The range of keys in two hfiles are
> overlapping to some extent, but not fully (so the two files are because of
> region merge).
> In such a case, depending on file sizes (used in
> StoreFile.Comparators.SEQ_ID), we may get different values for the same cell
> (say "r", "cf:50") depending on what we call: get "r" "cf:50" or get "r"
> "cf:".
> To replicate this, i ran ImportTsv twice with 2 different csv files but same
> timestamp (-Dimporttsv.timestamp=1). Collected two resulting hfiles in a
> single directory and loaded with LoadIncrementalHFiles. Here are the commands.
> {noformat}
> //CSV files should be in hdfs:///user/hbase/tmp
> sudo -u hbase hbase org.apache.hadoop.hbase.mapreduce.ImportTsv
> -Dimporttsv.columns=HBASE_ROW_KEY,c:1,c:2,c:3,c:4,c:5,c:6
> -Dimporttsv.separator='|' -Dimporttsv.timestamp=1
> -Dimporttsv.bulk.output=hdfs:///user/hbase/1 t tmp
> {noformat}
> tables_data.zip contains three tables: t, t2, and t3.
> To load these tables and test with them, use the attached
> TestWithSingleHRegion.java. (Change ROOT_DIR and TABLE_NAME variables
> appropriately)
> Hfiles for table 't':
> 1) 07922ac90208445883b2ddc89c424c89 : length = 1094: KVs = (c:5, 55) (c:6, 66)
> 2) 143137fa4fa84625b4e8d1d84a494f08 : length = 1192: KVs = (c:1, 1) (c:2, 2)
> (c:3, 3) (c:4, 4) (c:5, 5) (c:6, 6)
> Get returns 5 where as Scan returns 55.
> On the other hand if I make the first hfile, the one with values 55 and 66
> bigger in size than second hfile, then:
> Get returns 55 where as Scan returns 55.
> This can be seen in table 't2'.
> Weird things:
> 1. Get consistently returns values from larger hfile.
> 2. Scan consistently returns 55.
> Reason:
> Explanation 1: We add StoreFileScanners to heap by iterating over list of
> store files which is kept sorted in DefaultStoreFileManger using
> StoreFile.Comparators.SEQ_ID. It sorts the file first by increasing seq id,
> then by decreasing filesize. So our larger files sizes are always in the
> start.
> Explanation 2: In KeyValueHeap.next(), if both current and this.heap.peek()
> scanners (type is StoreFileScanner in this case) point to KVs which compare
> as equal, we put back the current scanner into heap, and call pollRealKV() to
> get new one. While inserting, KVScannerComparator is used which compares the
> two (one already in heap and the one being inserted) as equal and inserts it
> after the existing one. \[1\]
> Say s1 is scanner over first hfile and s2 over second.
> 1. We scan with s2 to get values 1, 2, 3, 4
> 2. see that both scanners have c:5 as next key, put current scanner s2 back
> in heap, take s1 out
> 4. return 55, advance s1 to key c:6
> 5. compare c:6 to c:5, put back s2 in heap since it has larger key, take out
> s1
> 6. ignore it's value (there is code for that too), advance s2 to c:6
> Go back to step 2 with both scanners having c:6 as next key
> This is wrong because if we add a key between c:4 and c:5 to first hfile, say
> (c:44, foo) which makes s1 as the 'current' scanner when we hit step 2, then
> we'll get the values - 1, 2, 3, 4, foo, 5, 6.
> (try table t3)
> Fix:
> Assign priority ids to StoreFileScanners when inserting them into heap,
> latest hfiles get higher priority, and use them in KVComparator instead of
> just seq id.
> \[1\]
> [PriorityQueue.siftUp()|http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/6-b14/java/util/PriorityQueue.java#586]
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