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Displaying posts with tag: gcache (reset)

How to calculate the correct size of Percona XtraDB Cluster’s gcache
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When a write query is sent to Percona XtraDB Cluster all the nodes store the writeset on a file called gcache. By default the name of that file is galera.cache and it is stored in the MySQL datadir. This is a very important file, and as usual with the most important variables in MySQL, the default value is not good for high-loaded servers. Let’s see why it’s important and how can we calculate a correct value for the workload of our cluster.

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Finding a good IST donor in Percona XtraDB Cluster 5.6
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Gcache and IST

The Gcache is a memory-based cache of recent Galera transactions that is local to each node in a cluster.  If a node leaves and rejoins the cluster, it can use the gcache from another node that stayed in the cluster (i.e., its donor node) to fetch the transactions it missed (IST) as opposed to doing a full state snapshot transfer (SST).  However, there are a few nuances that are not obvious to the beginner:

  • The Gcache is lost when a node restarts
  • The Gcache is fixed size and implemented as a LRU.  Once it is full, older transactions roll off.
  • Donor …
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Understanding gcache in Galera
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October 16, 2013 By Severalnines

Galera uses a preallocated file with a specific size called gcache, used to store the writesets in circular buffer style. By default, its size is 128MB. In this post, we are going to explore how to leverage gcache to improve the operation of a Galera cluster.

 

Test Case

 

We have a four node Galera cluster, using the latest release 23.2.7(r157). We have a table called t1 that is replicated by Galera on all nodes. The cluster nodes have allocated the default 128MB gcache.size, and we’ll try to execute …

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Showing entries 1 to 3

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