Re: [google-appengine] Re: Do HR-enabled apps get more than one memcached instance?
Thanks for the clarification. On 15 May 2011 00:47, Mike Wesner wrote: > Your app actually only runs out of one data center at once. The > diagram was a little misleading. If a data center goes down then your > app is served out of the other with a different memcache (empty) > > On May 14, 3:26 pm, Sergey Schetinin wrote: >> I'm pretty sure the memcached clusters (if there are more than one) >> are not synchronized. First of all, that would be way too slow. >> Second, the talk I referenced specifically mentions that when the apps >> are being migrated from a DC, the memcache writes return success but >> are in fact noop, because synchronizing memcache data does not make >> sense. So I would expect that there's no synchronization going on >> during regular operation as well. >> >> Anyway, I really hope that there's only one memcached cluster active at a >> time. >> >> On 14 May 2011 22:05, rekby wrote: >> >> >> >> >> >> >> >> >> >> > I thing HR-applications have more than one syncronised memcache - by >> > me test save in HR-memcache in 3 times slower, than Master/Slave >> > application. >> >> > On May 14, 6:56 pm, Sergey Schetinin wrote: >> >> So, I was watching the presentation on the HR datastore from the IO >> >> 2011 >> >> (http://www.google.com/events/io/2011/sessions/more-9s-please-under-th... >> >> ) and one thing caught my attention: the slides were showing the >> >> frontend instances running in more than one datacenter at the same >> >> time. So I understand that the memcached can lose data at any time and >> >> if the app is migrated between the datacenters all of the data in the >> >> cache are lost, however, running the app in two or more datacenters at >> >> a time each DC having a separate memcached cluster, that changes the >> >> properties quite significantly. >> >> >> For example let's consider an app that uses some memcached key to keep >> >> a cursor where to write to the datastore, atomically incrementing it >> >> after each write. Such an app can detect if such a key is not present >> >> in the cache and determine what the cursor is by doing a query on the >> >> database and then add it to the cache atomically. If we add the >> >> possibility that there's another DC running the app w/ an independent >> >> memcached instance, such an app would just corrupt its own data. >> >> >> I hope I explained my concern well enough, and I would love to hear an >> >> answer from someone on the App Engine team. >> >> >> Thank you. >> >> >> -Sergey >> >> >> --http://self.maluke.com/ >> >> > -- >> > You received this message because you are subscribed to the Google Groups >> > "Google App Engine" group. >> > To post to this group, send email to google-appengine@googlegroups.com. >> > To unsubscribe from this group, send email to >> > google-appengine+unsubscr...@googlegroups.com. >> > For more options, visit this group >> > athttp://groups.google.com/group/google-appengine?hl=en. >> >> --http://self.maluke.com/ > > -- > You received this message because you are subscribed to the Google Groups > "Google App Engine" group. > To post to this group, send email to google-appengine@googlegroups.com. > To unsubscribe from this group, send email to > google-appengine+unsubscr...@googlegroups.com. > For more options, visit this group at > http://groups.google.com/group/google-appengine?hl=en. > > -- http://self.maluke.com/ -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. To post to this group, send email to google-appengine@googlegroups.com. To unsubscribe from this group, send email to google-appengine+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en.
[google-appengine] Re: Do HR-enabled apps get more than one memcached instance?
Your app actually only runs out of one data center at once. The diagram was a little misleading. If a data center goes down then your app is served out of the other with a different memcache (empty) On May 14, 3:26 pm, Sergey Schetinin wrote: > I'm pretty sure the memcached clusters (if there are more than one) > are not synchronized. First of all, that would be way too slow. > Second, the talk I referenced specifically mentions that when the apps > are being migrated from a DC, the memcache writes return success but > are in fact noop, because synchronizing memcache data does not make > sense. So I would expect that there's no synchronization going on > during regular operation as well. > > Anyway, I really hope that there's only one memcached cluster active at a > time. > > On 14 May 2011 22:05, rekby wrote: > > > > > > > > > > > I thing HR-applications have more than one syncronised memcache - by > > me test save in HR-memcache in 3 times slower, than Master/Slave > > application. > > > On May 14, 6:56 pm, Sergey Schetinin wrote: > >> So, I was watching the presentation on the HR datastore from the IO > >> 2011 > >> (http://www.google.com/events/io/2011/sessions/more-9s-please-under-th... > >> ) and one thing caught my attention: the slides were showing the > >> frontend instances running in more than one datacenter at the same > >> time. So I understand that the memcached can lose data at any time and > >> if the app is migrated between the datacenters all of the data in the > >> cache are lost, however, running the app in two or more datacenters at > >> a time each DC having a separate memcached cluster, that changes the > >> properties quite significantly. > > >> For example let's consider an app that uses some memcached key to keep > >> a cursor where to write to the datastore, atomically incrementing it > >> after each write. Such an app can detect if such a key is not present > >> in the cache and determine what the cursor is by doing a query on the > >> database and then add it to the cache atomically. If we add the > >> possibility that there's another DC running the app w/ an independent > >> memcached instance, such an app would just corrupt its own data. > > >> I hope I explained my concern well enough, and I would love to hear an > >> answer from someone on the App Engine team. > > >> Thank you. > > >> -Sergey > > >> --http://self.maluke.com/ > > > -- > > You received this message because you are subscribed to the Google Groups > > "Google App Engine" group. > > To post to this group, send email to google-appengine@googlegroups.com. > > To unsubscribe from this group, send email to > > google-appengine+unsubscr...@googlegroups.com. > > For more options, visit this group > > athttp://groups.google.com/group/google-appengine?hl=en. > > --http://self.maluke.com/ -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. To post to this group, send email to google-appengine@googlegroups.com. To unsubscribe from this group, send email to google-appengine+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en.
Re: [google-appengine] Re: Do HR-enabled apps get more than one memcached instance?
I'm pretty sure the memcached clusters (if there are more than one) are not synchronized. First of all, that would be way too slow. Second, the talk I referenced specifically mentions that when the apps are being migrated from a DC, the memcache writes return success but are in fact noop, because synchronizing memcache data does not make sense. So I would expect that there's no synchronization going on during regular operation as well. Anyway, I really hope that there's only one memcached cluster active at a time. On 14 May 2011 22:05, rekby wrote: > I thing HR-applications have more than one syncronised memcache - by > me test save in HR-memcache in 3 times slower, than Master/Slave > application. > > On May 14, 6:56 pm, Sergey Schetinin wrote: >> So, I was watching the presentation on the HR datastore from the IO >> 2011 >> (http://www.google.com/events/io/2011/sessions/more-9s-please-under-th... >> ) and one thing caught my attention: the slides were showing the >> frontend instances running in more than one datacenter at the same >> time. So I understand that the memcached can lose data at any time and >> if the app is migrated between the datacenters all of the data in the >> cache are lost, however, running the app in two or more datacenters at >> a time each DC having a separate memcached cluster, that changes the >> properties quite significantly. >> >> For example let's consider an app that uses some memcached key to keep >> a cursor where to write to the datastore, atomically incrementing it >> after each write. Such an app can detect if such a key is not present >> in the cache and determine what the cursor is by doing a query on the >> database and then add it to the cache atomically. If we add the >> possibility that there's another DC running the app w/ an independent >> memcached instance, such an app would just corrupt its own data. >> >> I hope I explained my concern well enough, and I would love to hear an >> answer from someone on the App Engine team. >> >> Thank you. >> >> -Sergey >> >> --http://self.maluke.com/ > > -- > You received this message because you are subscribed to the Google Groups > "Google App Engine" group. > To post to this group, send email to google-appengine@googlegroups.com. > To unsubscribe from this group, send email to > google-appengine+unsubscr...@googlegroups.com. > For more options, visit this group at > http://groups.google.com/group/google-appengine?hl=en. > > -- http://self.maluke.com/ -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. To post to this group, send email to google-appengine@googlegroups.com. To unsubscribe from this group, send email to google-appengine+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en.
[google-appengine] Re: Do HR-enabled apps get more than one memcached instance?
I thing HR-applications have more than one syncronised memcache - by me test save in HR-memcache in 3 times slower, than Master/Slave application. On May 14, 6:56 pm, Sergey Schetinin wrote: > So, I was watching the presentation on the HR datastore from the IO > 2011 (http://www.google.com/events/io/2011/sessions/more-9s-please-under-th... > ) and one thing caught my attention: the slides were showing the > frontend instances running in more than one datacenter at the same > time. So I understand that the memcached can lose data at any time and > if the app is migrated between the datacenters all of the data in the > cache are lost, however, running the app in two or more datacenters at > a time each DC having a separate memcached cluster, that changes the > properties quite significantly. > > For example let's consider an app that uses some memcached key to keep > a cursor where to write to the datastore, atomically incrementing it > after each write. Such an app can detect if such a key is not present > in the cache and determine what the cursor is by doing a query on the > database and then add it to the cache atomically. If we add the > possibility that there's another DC running the app w/ an independent > memcached instance, such an app would just corrupt its own data. > > I hope I explained my concern well enough, and I would love to hear an > answer from someone on the App Engine team. > > Thank you. > > -Sergey > > --http://self.maluke.com/ -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. To post to this group, send email to google-appengine@googlegroups.com. To unsubscribe from this group, send email to google-appengine+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en.
