Anouncing new long term stable branch for CTDB: 1.13

[ronnie sahlberg]

List

Please find new CTDB branch 1.13 available.
This will be the new long term stable branch for CTDB and will start
undergoing testing and stabilization over the next few time-units.


The main new features in 1.13 are two significant performance
improvements for certain workloads :

* ReadOnly record support:  This is a new feature to introduce shared
read-locks for the ctdb database.
This greatly improves workloads where many processes are accessing the
same record concurrently.

An example workload that is improved by allowing shared-readlocks
would be brlock.tdb for the case where many processes are
reading/writing to the same file concurrently. This allows each node
to have a local readonly copy of the database record associated to the
file.

SMBTORTURE testing for worst case workload (hundreds of SMBDs all
reading from the same file) has shown performance improvements
exceeding 10x


* Fethc-Lock-Collapse: This is a new feature to rate-limit the number
of concurrent requests for an exclusive-writelock for a record and
improving scaling and performance.
This greatly improves performance and reduces cpu utilization for
common workloads where many clients are trying to write to the same
record in the database.
For example locking.tdb  with large number of clients opnening/closing
the same file concurrently.


In order to use/test  read-only records, you need a separate patch for
samba which will be posted separately.
The support is disabled by default but can be activated on a per
database basis using :

onnode all ctdb setdbreadonly brlock.tdb

ctdb getdbmap | grep brlock.tdb
dbid:0x4e66c2b2 name:brlock.tdb path:/var/ctdb/brlock.tdb.0 READONLY
<-- this means the support is activated.

doc/readonlyrecords.txt contains technical description on how they work.

regards
ronnie sahlberg