C.1. General | |
Are there other HBase FAQs? | |
See the FAQ that is up on the wiki, HBase Wiki FAQ as well as the Troubleshooting page. | |
Does HBase support SQL? | |
Not really. SQL-ish support for HBase via Hive is in development, however Hive is based on MapReduce which is not generally suitable for low-latency requests. See the Chapter 11, Data Model section for examples on the HBase client. | |
How does HBase work on top of HDFS? | |
HDFS is a distributed file system that is well suited for the storage of large files. It's documentation states that it is not, however, a general purpose file system, and does not provide fast individual record lookups in files. HBase, on the other hand, is built on top of HDFS and provides fast record lookups (and updates) for large tables. This can sometimes be a point of conceptual confusion. See the Chapter 11, Data Model and Chapter 12, Architecture sections for more information on how HBase achieves its goals. | |
Why are logs flooded with '2011-01-10 12:40:48,407 INFO org.apache.hadoop.io.compress.CodecPool: Got brand-new compressor' messages? | |
Because we are not using the native versions of compression libraries. See HBASE-1900 Put back native support when hadoop 0.21 is released. Copy the native libs from hadoop under hbase lib dir or symlink them into place and the message should go away. | |
C.2. EC2 | |
Why doesn't my remote java connection into my ec2 cluster work? | |
See Andrew's answer here, up on the user list: Remote Java client connection into EC2 instance. | |
C.3. Building HBase | |
When I build, why do I always get | |
Ignore it. Its not an error. It is officially ugly though. | |
C.4. Runtime | |
Loading, why do I see pauses when loading HBase? | |
If compression is enabled, see this thread up on the user list, Long client pauses with compression. | |
Why does my RegionServer hang inexplicitly? | |
Are you running an old JVM (< 1.6.0_u21?)? When you look at a thread dump,
does it look like threads are BLOCKED but no one holds the lock all are
blocked on? See HBASE 3622 Deadlock in HBaseServer (JVM bug?).
Adding | |
Why do I see double the actual count of regionservers, once by domain name and then by IP? | |
Fix your DNS. In versions of HBase before 0.92.x, reverse DNS needs to give same answer as forward lookup. See HBASE 3431 Regionserver is not using the name given it by the master; double entry in master listing of servers for gorey details. | |
C.5. How do I...? | |
Secondary Indexes in HBase? | |
For a useful introduction to the issues involved maintaining a secondary Index in a store like HBase, see the David Butler message in this thread, HBase, mail # user - Stargate+hbase |