Structs As Query Indexes, Speed, And Rick Osborne
For those of you who follow my blog, you will know that Rick Osborne is the guy who comes in after I explain things and makes killer suggestions about how they can be done better. I recently gave a case study of how ColdFusion code can be optimized. It involved using the IndexOf() method of the ColdFusion query column object. Rick came in and suggested that using a Struct to create your own query-index would perform faster. As I am a man who likes to learn by doing, I thought I would put this to the test.
To test this, I query from a web statistics program. I am getting information from two tables: web_stats_hit and web_stats_session. Each "hit" in the hits table will have a session id in the session table. The session table also have a UUID column "session_id".
As I am trying to test the merging of two data sources, I am going to hit each table individually and then try to update one with matching values from the other. First I am grabbing the two different data sets:
<!--- Query for web hits. ---> <cfquery name="qHit" datasource="..."> SELECT h.id, h.date_created, h.web_stats_session_id, ( '' ) AS session_id FROM web_stats_hit h </cfquery> <!--- Query for web sessions. ---> <cfquery name="qSession" datasource="..."> SELECT s.id, s.session_id FROM web_stats_session s </cfquery>
As I tried to explain earlier, for every qHit.web_stats_session_id, there is a matching session, such that for some combo, qHit.web_stats_session_id == qSession.id. And just to get an idea of the amount of data we are talking about:
qHit: 52,290 records
qSession: 34,753 records
That's a LOT of data to go through. Let's get our "test" on:
<cftimer label="IndexOf() Methodology" type="outline"> <!--- Loop over the hit query. ---> <cfloop query="qHit"> <!--- We want to find a matching session_id based on the session. Get index of matching row. ---> <cfset intIndex = qSession[ "id" ].IndexOf( JavaCast( "int", qHit.web_stats_session_id ) ) /> <!--- Add one to index (to be ColdFusion friendly). ---> <cfset intIndex = (intIndex + 1) /> <!--- Check to see if we have an index. ---> <cfif intIndex> <!--- We found the match, update the row. ---> <cfset qHit[ "session_id" ][ qHit.CurrentRow ] = qSession[ "session_id" ][ intIndex ] /> </cfif> </cfloop> </cftimer> <cftimer label="Struct Index Methodology" type="outline"> <!--- Create a session look up table. ---> <cfset objSessionLookUp = StructNew() /> <!--- Loop over session and set index rows. We will be using the id column of the session as the key and the session_id as the value. This creates our very own, in-memory index of the qSession query based on ID. ---> <cfloop query="qSession"> <!--- Index this value. ---> <cfset objSessionLookUp[ qSession.id ] = qSession.CurrentRow /> </cfloop> <!--- Loop over the hit query. ---> <cfloop query="qHit"> <!--- Check to see if the session key exists. If it does, then we found a match. ---> <cfif StructKeyExists( objSessionLookUp, qHit.web_stats_session_id )> <!--- Update the session based on the struct-index. ---> <cfset qHit[ "session_id" ][ qHit.CurrentRow ] = objSessionLookUp[ qHit.web_stats_session_id ] /> </cfif> </cfloop> </cftimer>
It turns out Rick was absolute correct. The struct index performs MUCH faster. Here are the stats:
IndexOf() Methodology : 402,037 ms
Struct Index Methodology : 33,403 ms
Some quick math will show you that the struct index method performs in 8% of the time that the IndexOf() methodology does. EIGHT PERCENT! Nuts. I guess the only downside is that you can potentially create a HUGE in-memory structure; but it's only temporary.
Nicely done Rick!
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