Okay,
when the featureId sets up the ranges to scan, I need to know the
featureId depends on.
I know that you use an own implemenation for a SimpleFeatureType,
but I can´t find the place where you determine the featureId from a
given SimpleFeature. I assume that you override the getId() method.
A featureID looks like this, which seems to have five parts
(separated by "-"):
909271fc-44fa-495b-b876-5843df987fef
The composition of these values reflects the
hierarchy of the index, isn´t it? (from coarse-grained to
fine-grained) If not, how do you determine the featureID? What are
these five parts?
Best regards,
Marcel Jacob.
Am 21.10.2015 18:26, schrieb Emilio
Lahr-Vivaz:
Hi
Marcel,
Executing a query is basically 3 steps:
1. Choose the best index to scan given the query
2. Set up the scan ranges, iterators, etc for the given index
3. Transform the results coming back from accumulo into
SimpleFeatures
- We use a cost-based strategy for picking an index to scan. Right
now it is fairly static, but we allow for user hints to indicate a
preferred strategy. The code for calculating costs is here:
https://github.com/locationtech/geomesa/blob/master/geomesa-accumulo/geomesa-accumulo-datastore/src/main/scala/org/locationtech/geomesa/accumulo/index/QueryStrategyDecider.scala
- We use the feature ID out of the index table in order to 'join'
against the record table. You can see that code snippet here:
https://github.com/locationtech/geomesa/blob/master/geomesa-accumulo/geomesa-accumulo-datastore/src/main/scala/org/locationtech/geomesa/accumulo/index/AttributeIdxStrategy.scala#L153-L154
- When scanning the records table, we only care about the Value -
that is the serialized simple feature, including ID. The row of
the record table has the feature ID in it, which is how we set up
a range to scan.
Hope that helps,
Emilio
On 10/21/2015 11:59 AM, Marcel wrote:
Hello all,
I´m struggling how the process of executing a query is done on a
theoretical level.
Could you explain how Geomesa executes this query (step by
step)?
Following points would be very interesting:
- Is there an order for the tables? (maybe look first at
attr_idx, then st_idx and finally full table scan if
needed...something like this).
- What is returned from the index table? (for mapping with
records table - maybe feature id?)
- What about the records table? (current structure of rowid -
including feature id?)
Best regards,
Marcel Jacob.
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