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testing Galera



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 cluster.

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 configuration.

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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