Hi geode-dev,
Some time ago I was working on allowing INDEX_THRESHOLD_SIZE System property to
override CompiledValue.RESULT_LIMIT.
After this change, adding this attribute will take into a count if you set it.
But I need some clarification of this INDEX_THRESHOLD_SIZE attribute. Why is
this set by default to 100?
The main problem with this attribute is that if you want to get the correct
result, you need to know how many entries will be in the region while starting
servers and set it on that value or higher. Sometimes it is too hard to know
how many entries will be in the region, so maybe better will be to set it by
default to some higher number, something like Integer.MAX_VALUE.
Where this attribute is used?
It is used to get index results while doing queries.
What is the problem?
If we have INDEX_THRESHOLD_SIZE set to 500, and we have 1k entries it can
happen that while doing a query it will get only 500 entries and where clause
cannot be fulfilled and we got no results.
Let's see it by an example!
We have only one entry that matches the condition from the query,
INDEX_THRESHOLD_SIZE set to 500, and 1k entries in the region.
If we run the query without an index we got the result.
gfsh>query --query="<trace>SELECT e.key, e.value from /example-region.entrySet
e where e.value.positions['SUN'] like 'someth%'"
Result : true
Limit : 100
Rows : 1
Query Trace : Query Executed in 10.750238 ms; indexesUsed(0)
key | value
--- |
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
700 |
{"ID":700,"indexKey":0,"pkid":"700","shortID":null,"position1":{"mktValue":1945.0,"secId":"ORCL","secIdIndexed":"ORCL","secType":null,"sharesOutstanding":1944000.0,"underlyer":null,"pid":1944,"portfolioId":700,..
If we create an index and then run again this query there is no result.
gfsh>query --query="<trace>SELECT e.key, e.value from /example-region.entrySet
e where e.value.positions['SUN'] like 'someth%'"
Result : true
Limit : 100
Rows : 0
Query Trace : Query Executed in 22.079016 ms; indexesUsed(1):index1(Results:
500)
This happened because we have no luck getting that entry that matches the
condition in the intermediate results for the index.
So the questions are:
What if more entries enter the region that will make the index return more
entries than this threshold sets? Then we're again in jeopardy that the query
condition will not match.
Why is this attribute set by default to 100?
Can we change it to the Integer.MAX_VALUE by default to be sure that we have
the correct result? What are the consequences?
BR,
Mario
