Hello all,
we are using GeoServer to display a large number of GeoTIFFs using
ImageMosaic data stores. The data has several dimensions (time and
custom). We are adding new data to these stores periodically and the
goal is to be able to display years of data (millions of granules). We
have encountered performance problems with the WMS GetCapabilities
operation. It is most noticeable when using Oracle database (or PostGIS
with parameter WrapStore=true). My colleague Ivan (in CC) implemented
changes which improved the performance for our use case significantly.
We would like to publish these changes and hopefully merge them into the
official repo.
Details:
our performance problems are caused by the queries for values and
defaults for dimensions. The currently used queries vary depending on
the selected presentation for the dimension:
1. query for values:
"List":
* PostGIS (with WrapStore=false): SELECT distinct("<dim_name>")
FROM "<table_name>"
* Oracle: SELECT FID, <DIM_NAME> FROM <table_name>
* PostGIS (with WrapStore=true): SELECT "fid","<dim_name>" FROM
"<table_name>"
First version is clearly the fastest, because it loads only
distinct values.
"Interval and resolution":
The queries are the same as for "List", but in this case we only
really need the min/max values, which could be calculated much faster in
the database.
2. query for defaults (when using smallest/biggest domain value):
* PostGIS (with WrapStore=false): SELECT <min | max> ("<dim_name>")
FROM "<table_name>"
* Oracle: SELECT FID, <DIM_NAME> FROM <table_name>
* PostGIS (with WrapStore=true): SELECT "fid","<dim_name>" FROM
"<table_name>"
Again the first PostGIS variant is clearly the fastest. Others load
all the values to the application where the min/max values are calculated.
Our proposed solution creates optimized queries depending on which
presentation and default setting is used for the dimension. The needed
additional information from the settings is sent to the lower level
functions using new RenderingHints. The goal of the optimized queries is
to load only the needed values from the database (usually what the
current PostGIS query does). Unit tests were also added.
We would like to get some feedback on this. Can I submit merge requests
(to both GeoTools and GeoServer) to review the code?
We are looking forward to any comments.
best regards,
Gyorgy Tomcsanyi
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