The RocksDB TTL database only honours the TTL when the database
is compacted. If the database is not compacted, stale values will
be returned until the end of time.
Here we utilize the knowledge that the TTL is stored after the
actual value and use the root database for getting the value,
thereby getting access to the timestamp.
It's still worthwhile using the TTL database as that'll give
us compaction and the removal of stale items.
RocksDB is cloned from github and version v4.9 (latest at the time of
this writing) is checked out.
RocksDB can only be compiled as C++11, which means that RocksDB and hence
storage_rocksdb can be built only if the GCC version is >= 4.7.
The actual storage implementation is quite straightforward.
- The key is a SHA512 of the entire query. That will be changed so that
the database/table name is stored in the beginning of the key unhashed
as that will cause cached items from the same table to be stored
together. Assumption is that if you access something from a particular
table, chances are you will access something else as well.
- When the SO is loaded, the initialization function will created a
subdirectory storage_rocksdb under the MaxScale cache directory.
- For each instance, the RocksDB cache is created into a directory
whose name is the same as the cache filter name in the configuration
file, under that directory.
- The storage API's get and put functions are then mapped directly on
top of RockDB's equivalent functions.
The different server monitoring functions all did similar work and
combining them into one function makes the whole process of monitoring a
server simpler.
If a relay master server is found in the replication tree, it should not
get the master status. Previously all master servers were assigned the
master status regardless of their depth in the replication tree.
By comparing the depth value of each potential master, the monitor can
find the right master at the root of the replication tree.
The mysqlmon now supports proper detection of multi-master topologies by
building a directed graph out of the monitored server. If cycles are found from
this graph, they are assigned a master group ID. All servers with a positive
master group ID will receive the Master status unless they have `@@read_only`
enabled.
This new functionality can be enabled with the 'multimaster' boolean
parameter.
Mysqlmon now stores the values of read_only, slave_sql_running,
slave_io_running, the name and position of the masters binlog and the
replication configuration status of the slave.
This allows more detailed server information to be displayed with the
`show monitor <name>` diagnostic interface. In addition to this, the new
structure used to store them provides an easy way to store information
that is specific to a monitor and the servers it monitors.
These new status variables can be used to implement better multi-master
detection in mysqlmon by using the value of read_only to resolve
situations where multiple master candidates are available.
The CHK_LOGFILE macro first asserts that the values being checked are
valid and then proceeds to evaluate it again. The result of this
evaluation was not assigned to anything and it caused GCC 6.1.1 to produce
a warning.
When a client executes commands which do not return results (for example
inserting BLOB data via the C API), readwritesplit expects a result for
each sent packet. This is a somewhat of a false assumption but it clears
itself out when the session is closed normally. If the session is closed
due to an error, the counter is not decremented.
Each sesssion should only increase the number of active operation on a
server by one operation. By checking that the session is not already
executing an operation before incrementing the active operation count the
runtime operation count will be correct.
If systemd restarts MaxScale when an abnormal exit is detected, it is
likely to happen again. This leads into a loop which causes multiple
maxscale processes on the same machine. One example of this behavior is
when systemd times MaxScale out when it is starting.
If the installation directory is something else than /usr,
then the directories
<install-dir>/var/cache/maxscale
<install-dir>/var/log/maxscale
<install-dir>/var/run/maxscale
will be created at installation time.
The document is now split into module type sections. Added documentation on the
limitations on multiple monitors monitoring the same servers and filters not
receiving complete packets when used with readconnroute.
Although claimed in the output of "--help", the long option
"--execdir" was not supported. Support for that now added.
The long options have now also been sorted in the same order
as the options are displayed by the help, to make it easy to
check that everything is there.
Further, the description column of the output of --help has
been aligned.
In the configuration section of services and monitors, the
password to be used can now be specified using 'password'
in addition to 'passwd'.
If both are provided, then the value of 'passwd' is used. That
way there cannot be any surprises, should someone for whatever
reason currently (in 1.4.3 an invalid parameter will not prevent
MaxScale from starting) have a 'password' entry in his config file.
In the next release 'passwd' can be deprecated and in the release
after that removed.
The service start retry mechanism mistakenly returned an error when a
service failed to start but a retry was queued. This caused MaxScale to
stop whenever a service failed to start.
dcb_count_by_usage did not iterate the list properly and would get stuck on the
first inactive DCB. Since this function is only called by maxinfo, it would be
the only one to get stuck.
