Re: [appengine-java] Possibility for race condition on datastore?
Thanks for the input. Transactions is exactly what I was looking for. I coding a small game where people can attack each other and decrease their hp. If players ended up quering for the players hp and different datastores contain different values, well that's not a good thing haha. I'm planning on using the memcache to store the players hp, but when the value is removed from the cache I got to get the newest value back into the memcache. On Thu, Mar 3, 2011 at 11:28 AM, Ikai Lan (Google) ika...@google.com wrote: Yes. The only way to correctly do this is with transactions and sharded counters. The better question, however, is this: what are you doing? Perhaps there is an alternative solution. Ikai Lan Developer Programs Engineer, Google App Engine Blog: http://googleappengine.blogspot.com Twitter: http://twitter.com/app_engine Reddit: http://www.reddit.com/r/appengine On Thu, Mar 3, 2011 at 10:57 AM, justin thekeyboard...@gmail.com wrote: I need to write code so that a user has a counter. This counter can be read, increase, and decrease. This counter is mission critical so I will use the high replication datastore. So lets say I create a counter entity which has a user entity as the ancestor. I increase the counter value and store the value. Almost simultaneously I get another request to read the counter. I get the entity from the datastore , using the correct ancestor chain, and I read the value. Is it possible that these two values will be different? If so, is there anyway way to prevent this from happening? -- You received this message because you are subscribed to the Google Groups Google App Engine for Java group. To post to this group, send email to google-appengine-java@googlegroups.com. To unsubscribe from this group, send email to google-appengine-java+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine-java?hl=en. -- You received this message because you are subscribed to the Google Groups Google App Engine for Java group. To post to this group, send email to google-appengine-java@googlegroups.com. To unsubscribe from this group, send email to google-appengine-java+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine-java?hl=en. -- You received this message because you are subscribed to the Google Groups Google App Engine for Java group. To post to this group, send email to google-appengine-java@googlegroups.com. To unsubscribe from this group, send email to google-appengine-java+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine-java?hl=en.
[appengine-java] Possibility for race condition on datastore?
I need to write code so that a user has a counter. This counter can be read, increase, and decrease. This counter is mission critical so I will use the high replication datastore. So lets say I create a counter entity which has a user entity as the ancestor. I increase the counter value and store the value. Almost simultaneously I get another request to read the counter. I get the entity from the datastore , using the correct ancestor chain, and I read the value. Is it possible that these two values will be different? If so, is there anyway way to prevent this from happening? -- You received this message because you are subscribed to the Google Groups Google App Engine for Java group. To post to this group, send email to google-appengine-java@googlegroups.com. To unsubscribe from this group, send email to google-appengine-java+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine-java?hl=en.
Re: [appengine-java] Possibility for race condition on datastore?
Yes. The only way to correctly do this is with transactions and sharded counters. The better question, however, is this: what are you doing? Perhaps there is an alternative solution. Ikai Lan Developer Programs Engineer, Google App Engine Blog: http://googleappengine.blogspot.com Twitter: http://twitter.com/app_engine Reddit: http://www.reddit.com/r/appengine On Thu, Mar 3, 2011 at 10:57 AM, justin thekeyboard...@gmail.com wrote: I need to write code so that a user has a counter. This counter can be read, increase, and decrease. This counter is mission critical so I will use the high replication datastore. So lets say I create a counter entity which has a user entity as the ancestor. I increase the counter value and store the value. Almost simultaneously I get another request to read the counter. I get the entity from the datastore , using the correct ancestor chain, and I read the value. Is it possible that these two values will be different? If so, is there anyway way to prevent this from happening? -- You received this message because you are subscribed to the Google Groups Google App Engine for Java group. To post to this group, send email to google-appengine-java@googlegroups.com. To unsubscribe from this group, send email to google-appengine-java+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine-java?hl=en. -- You received this message because you are subscribed to the Google Groups Google App Engine for Java group. To post to this group, send email to google-appengine-java@googlegroups.com. To unsubscribe from this group, send email to google-appengine-java+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine-java?hl=en.
