[HBASE-5128] [uber hbck] Online automated repair of table integrity and region consistency problems

• Type: New Feature
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 0.90.5, 0.92.0, 0.94.0, 0.95.2
• Fix Version/s: 0.94.0, 0.95.0
• Component/s: hbck
• Hadoop Flags: Reviewed

Release Note

HBaseFsck (hbck) has been updated with new repair capabilities. hbck is a tool for checking the region consistency and the table integrity invariants of a running HBase cluster. Checking region consistency verifies that .META., region deployment on region servers and the state of data in HDFS (.regioninfo files) all are in accordance. Table integrity checks verify that all possible row keys resolve to exactly one region of a table -- e.g. there are no individual degenerate or backwards regions; no holes between regions; and no overlapping regions. Previously hbck had the ability to diagnose inconsistencies but only had the ability to repair deployment region consistency problems. The updated version now has been augmented with the ability repair region consistency problems in .META. (by patching holes), repair overlapping regions (via merging), patch region holes (by fabricating new regions), and detecting and adopting orphaned regions (by fabricating new .regioninfo file if it is missing in a region's dir).

Caveats:
* The new hbck selects repairs assuming that HDFS as ground truth, the previous version treated .META. as ground truth.
* The hbck '-fix' option is present but deprecated and replaced with '-fixAssignments' option.
* This tool adds APIs in 0.90.7, 0.92.2 and 0.94.0 for clean repairs. The 0.90 version of the tool is compatible with HBase 0.90+, but may require restarting the master or individual individual regionserver for table enable/disable/delete commands to work properly.

• Assignee: Jonathan Hsieh
• Reporter: Jonathan Hsieh
• Created: 05/Jan/12 02:37
• Updated: 26/Feb/13 08:12
• Resolved: 23/Mar/12 23:56

Description

The current (0.90.5, 0.92.0rc2) versions of hbck detects most of region consistency and table integrity invariant violations. However with '-fix' it can only automatically repair region consistency cases having to do with deployment problems. This updated version should be able to handle all cases (including a new orphan regiondir case). When complete will likely deprecate the OfflineMetaRepair tool and subsume several open META-hole related issue.

Here's the approach (from the comment of at the top of the new version of the file).

/**
 * HBaseFsck (hbck) is a tool for checking and repairing region consistency and
 * table integrity.  
 * 
 * Region consistency checks verify that META, region deployment on
 * region servers and the state of data in HDFS (.regioninfo files) all are in
 * accordance. 
 * 
 * Table integrity checks verify that that all possible row keys can resolve to
 * exactly one region of a table.  This means there are no individual degenerate
 * or backwards regions; no holes between regions; and that there no overlapping
 * regions. 
 * 
 * The general repair strategy works in these steps.
 * 1) Repair Table Integrity on HDFS. (merge or fabricate regions)
 * 2) Repair Region Consistency with META and assignments
 * 
 * For table integrity repairs, the tables their region directories are scanned
 * for .regioninfo files.  Each table's integrity is then verified.  If there 
 * are any orphan regions (regions with no .regioninfo files), or holes, new 
 * regions are fabricated.  Backwards regions are sidelined as well as empty
 * degenerate (endkey==startkey) regions.  If there are any overlapping regions,
 * a new region is created and all data is merged into the new region.  
 * 
 * Table integrity repairs deal solely with HDFS and can be done offline -- the
 * hbase region servers or master do not need to be running.  These phase can be
 * use to completely reconstruct the META table in an offline fashion. 
 * 
 * Region consistency requires three conditions -- 1) valid .regioninfo file 
 * present in an hdfs region dir,  2) valid row with .regioninfo data in META,
 * and 3) a region is deployed only at the regionserver that is was assigned to.
 * 
 * Region consistency requires hbck to contact the HBase master and region
 * servers, so the connect() must first be called successfully.  Much of the
 * region consistency information is transient and less risky to repair.
 */

Issue Links

• duplicates: HBASE-4094 improve hbck tool to fix more hbase problem
• is depended upon by: HBASE-5781 Zookeeper session got closed while trying to assign the region to RS using hbck -fix
• is depended upon by: HBASE-5634 document how to use uberhbck
• is related to: HBASE-1621 merge tool should work on online cluster
• is related to: HBASE-4379 [hbck] Does not complain about tables with no end region [Z,]
• relates to: HBASE-5599 [hbck] handle NO_VERSION_FILE and SHOULD_NOT_BE_DEPLOYED inconsistencies
• relates to: HBASE-5719 Enhance hbck to sideline overlapped mega regions
• relates to: HBASE-5628 Improve performance of uberhbck
• relates to: HBASE-5630 hbck should disable the balancer using synchronousBalanceSwitch.
• requires: HBASE-5563 HRegionInfo#compareTo should compare regionId as well
• requires: HBASE-5588 Deprecate/remove AssignmentManager#clearRegionFromTransition
• requires: HBASE-5589 Add of the offline call to the Master Interface