Hi Nick,
Thanks for your fast answer!
Nick Johnson (Google) wrote:
Hi Ulrich,
On Wed, Feb 17, 2010 at 5:30 PM, Ulrich <[email protected]
<mailto:[email protected]>> wrote:
Hi,
I have read the following
"Timeouts due to datastore issues --- [...] The most common example of
this occurs when you are rapidly inserting a large number of entities
of the same kind, with auto-generated IDs. In this case, most inserts
hit the same range of the same tablet, and the single tablet server is
overwhelmed with writes. [...] If this does affect your app, the
easiest solution is to use more evenly distributed IDs instead of the
auto-allocated ones [...]"
(
http://code.google.com/appengine/articles/handling_datastore_errors.html
)
Let's say I am having a model "Parent" and a model "Child". For Parent
entities, I use key names that are evenly distributed. For Child
entities, I use auto-generated key IDs and _no_ key names, but all
Child entities are children of Parent entities, so the paths to the
children contain the evenly distributes key names of the parents.
If I have many write operations on children that are in the same
entity group, the described error could occur. But what happens if my
write operations are on children that are in different entity groups?
Their IDs are auto-generated and not evenly distributed, but their
paths contain the evenly distributed key names.
Good question! The point being made in the article refers to the
global distribution of the complete key, so writes to these children
will be well distributed, and you won't have to worry about this
source of contention.
-Nick Johnson
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