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From Apache Wiki <wikidi...@apache.org>
Subject [Hadoop Wiki] Trivial Update of "Hbase/MasterRewrite" by stack
Date Sat, 12 Sep 2009 22:42:02 GMT
Dear Wiki user,

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The following page has been changed by stack:

The comment on the change is:
Initial upload of notes from hackathon

New page:
= Design Notes for [https://issues.apache.org/jira/browse/HBASE-1816 Master Rewrite, HBASE-1816]
for hbase 0.21.0 =

The notes below grew out of conversation had at the hbase hackathon held at StumbleUpon, August
5-7, 2009 (Jon Gray kept notes.  TODO: Link to them when posted).

== What does the Master do now? ==
 * Splitting
  * Should be distributed
 * Region Assignment
  * Balancing
 * Scan root/meta
  * Make sure Regions are online
  * Delete parents if no reference
 * Manage schema alter/online/offline
 * Admin
  * Close region
  * Flush
  * Compact/Major compact
 * Watches ZK for its own lease and for regionservers so knows when to run recovery

== Design ==

== Notes ==
To be organized...

For RS Worst case loading calculation
 * 200 regionservers
 * 32 logs per regionserver
 * 200 regions written to
 * 2GB or 30 hour full log roll
 * 10MB/sec write speed
 * 1.2M edits per 2G
  * 7k writes/second across cluster (?) -- whats this?  Wrong.
 * 1.2M edits per 30 hours?
  * 100 writes/sec across cluster (?) -- Whats this?  Wrong?

Assignment / balancing
 * RS publish load into ZK
  * /hbase/rsload/startcode({‘json’:’load’})
  * Configure period it is refreshed
 * Assignment inputs
  * Load
  * Requests / sec
  * regions online
 * Distribute tables randomly across cluster
  * Never give table back to who unassigned it
  * During split, bottom half to the same server, top half reassigned
 * Assignment Queue
  * Candidate Queue
   * Master watches ZK candidate queue /hbase/rsassign/region(last_owned_by_rs)
   * When new nodes come in, it assigns the out Regionservers put regions into the candidate
queue when they unassign/close
 * To Open Queue
  * Regionservers watch their own to open queues /hbase/rsopen/region(extra_info, which hlogs
to replay or it’s a split, etc)

Administrative functions
 * Hadoop RPC listeners on Master and Regionservers -- master can now push messages
 * Clients and Master can talk to RS

Safe-mode assignment
 * Collect all regions to assign
 * Randomize and assign out in bulk, one msg per RS
 * Region assignment is always
  * Look at all regions to be assigned
  * Make a single decision for the assignment of all of these

 * New feature in ZK
  * Sorted tree or list node
  * Has a getClosestBefore / getRegionForRow(row)
  * META location stored in ZK
  * META table now only contains historian information
  * All other in ZK

No more ROOT

Worker pool region closing
 * Parallel flushes

 * Process server shutdown after RS crash
  * Separate META scan?
  * To figure out regions on an RS
   * Separate map of RS -> region
  * Trade-off between two-writes during assignment

Table Schema Information
 * Online schema edits?
  * If complex, punt to 0.22
  * Rather than storing with each region, stored once in ZK

Uptime on UI

Admin stuff
  * Straight from client ->regionserver
  * No more heartbeat piggyback

Scaling documentation
 * More conf settings for block cache
 * How to adjust knobs

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