Datastore Read Operations Calculation

Question

So I am currently performing a test, to estimate how much can my Google app engine work, without going over quotas. This is my test:

• I have in the datastore an entity, that according to my local dashboard, needs 18 write operations. I have 5 entries of this type in a table.
• Every 30 seconds, I fetch those 5 entities mentioned above. I DO NOT USE MEMCACHE FOR THESE !!!

That means 5 * 18 = 90 read operations, per fetch right ? In 1 minute that means 180, in 1 hour that means 10800 read operations..Which is ~20% of the daily limit quota...

However, after 1 hour of my test running, I noticed on my online dashboard, that only 2% of the read operations were used...and my question is why is that?...Where is the flaw in my calculations ?

Also...where can I see in the online dashboard how many read/write operations does an entity need?

Thanks

Answer 1

A write on your entity may need 18 writes, but a get on your entity will cost you only 1 read.

So if you get 5 entries every 30 secondes during one hour, you'll have about 5reads * 120 = 600 reads.

This is in the case you make a get on your 5 entries. (fetching the entry with it's id) If you make a query to fetch them, the cost is "1 read + 1 read per entity retrieved". Wich mean 2 reads per entries. So around 1200 reads in one hour.

For more details informations, here is the documentation for estimating costs.

You can't see on the dashboard how many writes/reads operations an entity need. But I invite you to check appstats for that.