While you can use the database client to check the status of your cluster, the individual nodes and the health of replication, you may find it counterproductive to log into the client on each node to run these checks. Galera Cluster provides a notification script and interface for customization, allowing you to automate the monitoring process for your cluster.
Snabb (formerly "Snabb Switch") is a simple and fast packet networking toolkit.
We are also a grassroots community of programmers and network engineers who help each other to build and deploy new network elements. We care about practical applications and finding simpler ways to do things.
One of our customers had a question related to the right value of Galera Cache size (gcache.size) in Galera Cluster for MySQL which I would like to share with you.
The question was: My maintenance window takes 4 hours for my 5TB DB. How can I avoid an SST ?!
Basically, having too small GCache size will lead to SST (Snapshot State Transfer) instead of IST (Incremental State Transfer), thus we can avoid the SST by setting the GCache to the appropriate value.
State Snapshot Transfer (SST) is a way for Galera to transfer a full data copy from an existing node (donor) to a new node (joiner). If you come from a MySQL replication background, it is similar to taking a backup of a master and restoring on a slave. In Galera Cluster, the process is automated and is triggered depending on the joiner state.
SST can be painful in some occasions, as it can block the donor node (with SST methods like mysqldump or rsync) and burden it when backing up the data and feeding it to the joiner. For a dataset of a few hundred gigabytes or more, the syncing process can take hours to complete - even if you have a fast network. It might be advisable to avoid e.g. when running in WAN environments with slower connects and limited bandwidth, or if you just want a very fast way of introducing a new node in your cluster.
To give you a little bit of background when the OSD writes into his journal it uses D_SYNC and O_DIRECT. Writing with O_DIRECT bypasses the Kernel page cache, while D_SYNC ensures that the command won’t return until every single write is complete. So yes, basically the OSD forces all the writes to be flushed prior to start the next IO.
s I plan to move from a proprietary calendaring to a more „ressource-aware” open source solution, I decided to give Radicale a try. It is open source, appears to be rather pragmatic in its approach to „standards” and has a small footprint in regards to system requirements.
With me running Debian 8 on my server, I decided to stick with the available package and not install „from source”. So a quick „apt-get install radicale” took care of installing the necessary software (do not forget to enable the Radicale daemon in /etc/default/radicale).
The configuration of Radicale is rather straightforward and simple. In regards to transport security, You can reuse an existing TLS certificate (or get a new one from Let’s encrypt). For authentication, you can choose between several options. As I don’t have an LDAP server (yet) and I didn’t want to create a .httpasswd entry for each user, I chose „IMAP”. So Radicale will validate all credentials against the local IMAP server (Dovecot in my case).
I did the backup using TWRP, transferred it to my laptop, wiped the device, sent it in, got it back, copied the backup to the phone, restored it and... Was locked out of the device, it would not take my password anymore. Well, it seems that happens, just delete some files and it will be fine.
Back in the days when somebody said MySQL, there was only the MySQL. You could pick different versions (4.0, 4.1) but the vendor was the same. This changed around MySQL 5.0/5.1 when Percona decided to release their own flavour of MySQL - Percona Server. A bit later, MariaDB joined with MariaDB 5.1 and the fun (or confusion) increased. What version should I use? What is the difference between MySQL 5.1, Percona Server 5.1 and MariaDB 5.1? Which one is faster? Which one is more stable? Which one has superior functionality? With time, this got worse as more and more changes were introduced in each of flavours. This blog post will be our attempt to summarize the key features that differentiate them. We will also try to give you some suggestions about which flavour may be the best for a given type of project. Let’s get started.
This article details my experiment on the matter. It is partly based on first hand experience, but also links to various other tutorials that helped me along the way. Especially thanks to folks on various IRC channels that really helped me out in understanding this.
There were a couple of QEMU / virtualization related talks at the DevConf 2017 conference that took place at the end of January already, but so far we missed to gather the links to the recordings of these talks. So here is now the list:
In this post I will explain how to transfer a multi terabyte size database between two MySQL instances using mydumper, which is a logical backup and restore tool that works in parallel. I will also cover the case where you need to transfer only a subset of data.
Big tables are often problematic because of the amount of time needed to do mysqldump/restore which is single threaded. It is not uncommon for this type of process to take several days.
n a perfect world, one would upgrade databases one version at a time and not let them get too old. But our databases are where the “crown jewels” are. They must stay up 24×7. When performance is acceptable, it’s acceptable, and sometimes old versions stay around too long. We don’t live in a perfect world. This idea applies to so many things. There’s almost never a perfect data model. There is always some type of resource constraint be it storage, memory, CPU, IOPS, or just plain dollars.
I will bring this concept of not living in a perfect world into a discussion about upgrades.
Ideally there would be…
- …time to do two upgrades. One upgrade to 5.6, the other to 5.7. This is the way sane, normal people upgrade.
- …a lot of extra hardware. It sure would be nice to maybe combine a maintenance like this with a hardware refresh so that we could just have an entirely new MySQL 5.7 database shard, slap a MySQL 5.6 box in the middle as a relay, and once things are all caught up just do a VIP cutover to new machines.
The extra hardware idea I have actually worked with in the past. A client of a company I worked for just had a standalone 5.5 machine with no replicants. They were able to allocate two more servers, one to be a 5.6 relay and one new 5.7 machine that would serve as a final destination. Added bonus… At the end the 5.6 server would be upgraded and left in place for a redundant machine.
MyCLI is a command line interface for MySQL, MariaDB, and Percona with auto-completion and syntax highlighting.