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Re: testing Galera


Hi Jan,

I recommend to ask for advice regarding Galera fine-tuning and tricks on the Codership mail list: codership-team@xxxxxxxxxxxxxxxx. It's an active group, and as far as I can tell, Galera experts there are quite responsive.

While we might be able to provide _some_ views on the subject, Codership people have far more intimate knowledge of Galera internals and specifics, and besides there are subscribers with different working configurations and environments, possibly in some cases similar to yours, so they might share their experience.


On 2/11/2013 7:38 PM, Jan Kirchhoff wrote:
Hi everybody,

I installed Galera on 2 servers, imported a database dump (took almost 2
days to import a 100GB gzipped sql-dump ...) and set up one of the two
servers as a replication slave of our main database.

Now as I try to understand all the new variables and want to get an idea
of do's and dont's some questions pop up:

While the traditional replication slave on the first galera-server is
still catching up (still 200000 seconds behind...) I had our main
data-proxy starting to write to that server.
Most of the data coming into our databases is not going its way trough
the replication but via our self-written proxy application. This
application connects to all databases, sets SQL_LOG_BIN=0 and then
starts updating just a few tables (up to 15-20GB of pure sql statements
per hour depending on the time of the day). This works fine, the server
was processing the statements no slower than the other non-galera servers.

I couldn't see the updates on the second galera-server and figured that
was because of the SQL_LOG_BIN=0. Now things got complicated. How to
resolve this? I gave it a try, hacked the proxy not to set SQL_LOG_BIN=0
for that specific server and started it again, but this made the second
server crash almost immidiatly with HA_ERR_KEY_NOT_FOUND - actually  I
was expecting something like that to happen as the tables were out of
sync now.

Is there something like slave_skip_counter, aka "I Know what I do, skip
that update"? I think I have to take a new snapshot to get the second
node up and consistent again. It tried to to that automatically but
stopped because of the hanging rsync-daemon problem. I'll let it catch
up with the replication lag first and then start that again...

If I take a node down or just restart mariadb after changing variables,
it pulls the changes it missed (IST) from another server, right? These
are saved in the galera-cache on all servers? How do I figure out what a
reasonable size for the gcache would be for me? The default size of
128MB is way to small for me if I want to take a node down for a few
hours to do backups/upgrades/whatever, but do I need 5, 10 or 50 GBs?
Some information on number of bytes written to the gcache I could look
at? Or is "wsrep_replicated_bytes" the number to look at?

Finding all documentation and understanding the details is a little bit
difficult and time-consuming, but I'm making my way...

btw: is maria-developers a better place to post this as I am not writing
on production software but alpha releases?


Am 28.01.2013 17:18, schrieb Jan Kirchhoff:

regarding the transaction rates: we currently have a peak at around
400-500/sec at certain times of the day. We'll see how that works

I just found there are no mariadb-galera-debs around for ubuntu 12.10.
Can we expect them soon? Otherwise I'd have to reinstall the test
servers with 12.04 - couldn't get the dependency problems resolved when
trying to get the 12.04-debs into 12.10 and I don't want to compile
myself :-(


Am 25.01.2013 10:24, schrieb Alex Yurchenko:
Hi Jan,

1) the load and the database size you described is nothing special to
Galera, we have users running it on bigger databases and with higher
transaction rates, Specifically those bulk inserts are perfectly fine.

2) notice that to get most of Galera (e.g. parallel applying) you have
to use ROW binlog format at least on all Galera nodes. Using
statement-based replication from master should be fine, but inside
Galera cluster it should be ROW.

3) your plan looks fine, just don't forget to set log_slave_updates when
mixing Galera and native MySQL replication.

4) the latest MariaDB-Galera has support for xtrabackup for new node


On 2013-01-24 00:09, Jan Kirchhoff wrote:

I'd like to evaluate mariadb-galera on some test databases. Our load
is at least 90% writes coming from a datastream and I would try to set
up a real-world situation and test with real data.
Most of the work load is "insert ... on duplicate key update"
mass-inserts (actually updates) of about 4MB/10000 rows each. 99% of
these run onto 3-4 tables (each around 10GB/7 million rows of size).
Total database size is around 800 GB.
We have a traditional statement-based master-slave replication, but
all these mass-inserts run over a proxy with SET SQL_LOG_BIN=0 in
parallel on all systems - no way to process this amount of data
single-threaded on the slaves. I was hoping galera would make this
easier and make our proxies obsolete.

I have some servers I could use for galera as a first step. I wanted
to do this for 4 months now but never got into it, I read your request
to test the RC and think I should start now hoping to be able to give
some valuable feedback:

After reading through the documentation and some blogs I have some
doubts, but my idea was to do the following:
I'd clone the database of an existing slave to a new machine with
mariadb-galera (name the host "testgalera1" and rsync the database or
use mysqldump). I'd then set up this one as a "normal" statement based
slave connected to one of our masters? Afterwards, the next host
"testgalera2" would have to be added to the galera-cluster? And after
that, I'd set up one of our older database servers and add that to the
cluster, too. My idea was to take an older, slower system to see how
much this slowes the cluster down and get an idea how much headroom
I'd have when I leave those old machines out (the old machines have
only 64GB of RAM and slower CPUs).

I'd then modify my proxy for all the incoming inserts and add a
writer-thread to one of the hosts in the cluster, that data should be
replicated by galera to all other galera hosts. All other data should
be coming in via the "traditional" replication thread of testgalera1.
This should give me a 95-99% real world write situation on the

Adding a host to a running cluster would mean cloning the whole
database (of course), but this also means the host I copy from would
have to block write access to its tables and buffer all modifications
in memory (at least that's how I read the documentation) during the
copy process. Looking at the database size and amount of inserts, I am
afraid adding a host to the cluster without taking everything down
would be impossible - or even if it works fine now it could cause
trouble once the database gets just a little bit larger or my load
increases a bit.

before I start with this - is galera an insane idea regarding my
load? Or is it worth a try?


some numbers of some of the old databases:

innodb_buffer_pool_size between 60-120 GB depending on server memory

db5: Uptime: 8052248  Threads: 44  Questions: 1413881794  Slow
queries: 160049  Opens: 683779  Flush tables: 2  Open tables: 1024
Queries per second avg: 175.588

db6: Uptime: 8070552  Threads: 6  Questions: 873413218  Slow queries:
3208  Opens: 336584  Flush tables: 1  Open tables: 578 Queries per
second avg: 108.222

db7: Uptime: 4175032  Threads: 28  Questions: 639627677  Slow
queries: 139337  Opens: 522673  Flush tables: 1  Open tables: 2016
Queries per second avg: 153.203

db7# mysql -e 'show global status like "%com\_%" ' |grep -v '\s0$'
Variable_name    Value
Com_admin_commands    289127
Com_alter_table    6269
Com_analyze    725
Com_begin    3712141
Com_change_db    80112
Com_commit    3999309
Com_create_db    1
Com_create_table    253849
Com_create_trigger    10
Com_create_view    68
Com_delete    12365037
Com_delete_multi    7
Com_drop_table    310771
Com_drop_trigger    10
Com_drop_view    65
Com_empty_query    509
Com_flush    48
Com_grant    36
Com_insert    314280963
Com_insert_select    613565
Com_kill    214
Com_lock_tables    85
Com_optimize    1
Com_purge    2320
Com_rename_table    11
Com_repair    1
Com_replace    14240825
Com_replace_select    29920
Com_revoke    8
Com_rollback    13
Com_select    178540996
Com_set_option    6886915
Com_show_binlogs    69960
Com_show_charsets    1542
Com_show_collations    1544
Com_show_create_db    28
Com_show_create_func    195
Com_show_create_table    53282
Com_show_create_trigger    1
Com_show_databases    43584
Com_show_events    3
Com_show_fields    131874
Com_show_function_status    45
Com_show_grants    335
Com_show_keys    2582
Com_show_master_status    142
Com_show_plugins    7224
Com_show_procedure_status    45
Com_show_processlist    116918
Com_show_slave_status    83193
Com_show_status    155732
Com_show_storage_engines    25
Com_show_table_status    7439
Com_show_tables    1973739
Com_show_triggers    538
Com_show_variables    85034
Com_show_warnings    766
Com_stmt_close    363
Com_stmt_execute    363
Com_stmt_prepare    363
Com_truncate    452
Com_unlock_tables    79
Com_update    34496744
Com_update_multi    408212

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