readable query is slow, fast query is un-readable

[hartmut bischoff]

Hi,  

in a previous mail, I attached a test-database with 

• a timegraph 'jahr', 'monat' 'tag' 
• a class 'bar'
• edges with a property "asset" pointing to a record in a class 'contract'

There is also some inherence : ohcl<- price <- midpoint, volatility  and so on.

The Idea is, to define ranges at the timegraph and investigate the properties of the connected vertices, which belong to some asset.

This is the basic graph

tag -- (out) -- ohlc -- (in) -- bar

In order to query for all data present for a contract (#58:2), 

My first attempt was a  simple direct query:

select expand(out('ohlc')) from tag where out('ohlc).asset = #58:2

unfortunately, an empty set was returned

However, changing to 

select expand(out('ohlc')) from tag where out_midpoint.asset = #58:2

leads to the correct result. 

Question: Is it possible to query inherent edges in this way?

I was very surprised: The query took 0.5 sec, with just a few records in the database.

The query took so long, because the hole time-graph was examined, as explain revealed: documentReads: 55152 

After some thinking, I came out with 

select expand(out('ohlc')) from (select expand(out) from ohlc where asset= #58:2 )

which fetches an identical result but is almost un-readable.  It is 10 times faster: 0,068 sec. 

My question is: Is it possible to write a human readable query without loosing to much performance? I couldn't figure out a solution using the match statement, so maybe there is another solution.  

A last thing: How can I determine the effects of scaling in terms of the execution time of the query. I wonder, whether my query will be as slow, if some hundred contracts and some million bars are present in the database, whereas the first attempt has probably a static execution time.

Thanks in advance

hartmut

10255010010005000

[Luca Garulli]

Have you tried with: 

select expand(out().out('ohlc')) from ohlc where asset= #58:2

Best Regards,

Luca Garulli

Founder & CEO

OrientDB LTD

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