Using a shared / mounted block storage with Xodus

Question

Is it safe to use mounted block storage as the Xodus database path? The idea is to run the application that uses Xodus in several different hosts. So each Xodus-based application is pointing to the same mounted path (e.g /mnt/xodus)

In this case, each application opens the Xodus environment like in the code below. If we open the environment like this:

  @Override
  public Environment getEnvironment(String xodusRoot, String instance) {
    Environment environment = environmentMap.get(xodusRoot + instance);
    if (environment == null) {
      EnvironmentConfig config = new EnvironmentConfig();
      config.setLogCacheShared(false);
      Environment env = Environments.newInstance(xodusRoot + instance, config);
      environmentMap.put(xodusRoot + instance, env);
    }
    Environment e = environmentMap.get(xodusRoot + instance);
    return e;
  }

Is it safe for multiple Xodus instances to point to a mounted path?

Please elaborate on "Is it safe?". That question is way too broad. — Progman, Nov 09 '19 at 09:21

Vyacheslav Lukianov · Accepted Answer · 2019-11-15T15:06:21.700

1

It depends on what particular block storage do you use. E.g., Xodus runs on Amazon EBS quite well, but EBS won't allow to share database files. If a block storage is shareable, then any opened Environment will be locked, so you have to somehow "shard" environment paths among hosts in order to prevent open conflicts. Probably, one can try to open Environments in read-only listening mode, but it would work only if the block storage can produce suitable file system events.

In addition, setting config.setLogCacheShared(false) would result in OOME if using several environments within single JVM.

edited Nov 15 '19 at 15:06

answered Nov 12 '19 at 15:56

Vyacheslav Lukianov

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I want to understand why it would throw out of memory error – quarks Nov 18 '19 at 00:00
If you switch off shared log cache (default option), then you have to control memory usage for each environment individually, In applications that can open arbitrary number of environments, this memusage control is rather difficult and finally not that efficient as default one. – Vyacheslav Lukianov Nov 18 '19 at 09:15

Using a shared / mounted block storage with Xodus

1 Answers1