How to improve performance of mongo simple search query - mongodb

Question

This is explanation of a simple search in mongodb, its taking more than 2.4 secs and more to retrieve data.If i add index(search params) it takes more than 5 secs.
Query
db.CX_EMPLOYEES.find({ "$or" : [{ "AML_FULLNAME" : /RAJ/ },
{ "AML_FULLALIAS" : /RAJ/ }] })
Explain
{
"cursor" : "BasicCursor",
"isMultiKey" : false,
"n" : 79,
"nscannedObjects" : 504570,
"nscanned" : 504570,
"nscannedObjectsAllPlans" : 504570,
"nscannedAllPlans" : 504570,
"scanAndOrder" : false,
"indexOnly" : false,
"nYields" : 0,
"nChunkSkips" : 0,
"millis" : 2423,
"indexBounds" : {},
"server" : "SERVER:27017"
}

Answer 1

Scheduled for the 2.6 version of MongoDb is a full text search feature. It's available as a development preview in current builds if enabled.
Given the nature of your query, it's likely to be the only option that might be effective using only MongoDb. As you're trying to do a "string contains" search according to the regular expressions you provided, the performance of doing a search to match strings on multiple fields will be terrible given the size of your collection. While it's a simple query in concept, translation to an efficient query is very difficult. Mongo needs to scan every document for a match. Breaking the words apart doesn't help, as Mongo still needs to scan every document.
If you can anchor the regular expression which means it would change to a "string starts with" rather than "string contains", the performance should be reasonable if you normalize the strings so that all character case is ignored, and realizing that matches will be exact still. For example, a is not á and would need to be specially handled.
Mongo's support for this type of query really are limited for production use. You may find that the full text search feature isn't suitable either. If this query is important, I'd suggest considering alternative search mechanisms. Possibly looking at something like Elastic Search for example.

Answer 2

There are no any reasons to add index on this search params because you using regExp. Index can improve find with regExp only if regExp has an anchor for the beginning.
db.CX_EMPLOYEES.find({ "$or" : [{ "AML_FULLNAME" : /^RAJ/ }, { "AML_FULLALIAS" : /^RAJ/ }] })
From documentation:
$regex can only use an index efficiently when the regular expression has an anchor for the beginning (i.e. ^) of a string and is a case-sensitive match. Additionally, while /^a/, /^a.*/, and /^a.*$/ match equivalent strings, they have different performance characteristics. All of these expressions use an index if an appropriate index exists; however, /^a.*/, and /^a.*$/ are slower. /^a/ can stop scanning after matching the prefix.

Answer 3

There is not a lot of things you can do. You have half of a million elements and you are doing full scan on all of them. Not a surprise that it takes time. Moreover your search is based on regex which can be anywhere in the string. So indexes can not help you in this case.
If your search is based on words, you can try to create array from the string. For example string 'Salvador Domingo Dali' will be converted to ['Salvador', 'Domingo', 'Dali']. If you will add an index on this array and will try to look for 'Dali', that the search will take advantage of this index.
P.S. databases and indexes are not a silver bullet. Sometimes you need a better logic to be able to deal with a lot of data.