Entity, dealing with large number of records (> 35

问题:

We have a rather large set of related tables with over 35 million related records each. I need to create a couple of WCF methods that would query the database with some parameters (data ranges, type codes, etc.) and return related results sets (from 10 to 10,000 records).

The company is standardized on EF 4.0 but is open to 4.X. I might be able to make argument to migrate to 5.0 but it's less likely.

What’s the best approach to deal with such a large number of records using Entity? Should I create a set of stored procs and call them from Entity or there is something I can do within Entity?

I do not have any control over the databases so I cannot split the tables or create some materialized views or partitioned tables.

Any input/idea/suggestion is greatly appreciated.

回答1:

At my work I faced a similar situation. We had a database with many tables and most of them contained around 7- 10 million records each. We used Entity framework to display the data but the page seemed to display very slow (like 90 to 100 seconds). Even the sorting on the grid took time. I was given the task to see if it could be optimized or not. and well after profiling it (ANTS profiler) I was able to optimize it (under 7 secs).

so the answer is Yes, Entity framework can handle loads of records (in millions) but some care must be taken

1. Understand that call to database made only when the actual records are required. all the operations are just used to make the query (SQL) so try to fetch only a piece of data rather then requesting a large number of records. Trim the fetch size as much as possible
2. Yes, not you should, you must use stored procedures and import them into your model and have function imports for them. You can also call them directly ExecuteStoreCommand(), ExecuteStoreQuery<>(). Sames goes for functions and views but EF has a really odd way of calling functions "SELECT dbo.blah(@id)".
3. EF performs slower when it has to populate an Entity with deep hierarchy. be extremely careful with entities with deep hierarchy .
4. Sometimes when you are requesting records and you are not required to modify them you should tell EF not to watch the property changes (AutoDetectChanges). that way record retrieval is much faster
5. Indexing of database is good but in case of EF it becomes very important. The columns you use for retrieval and sorting should be properly indexed.
6. When you model is large, VS2010/VS2012 Model designer gets real crazy. so break your model into medium sized models. There is a limitation that the Entities from different models cannot be shared even though they may be pointing to the same table in the database.
7. When you have to make changes in the same entity at different places, try to use the same entity by passing it and send the changes only once rather than each one fetching a fresh piece, makes changes and stores it (Real performance gain tip).
8. When you need the info in only one or two columns try not to fetch the full entity. you can either execute your sql directly or have a mini entity something. You may need to cache some frequently used data in your application also.
9. Transactions are slow. be careful with them.

if you keep these things in mind EF should give almost similar performance as plain ADO.NET if not the same.

回答2:

My experience with EF4.1, code first: if you only need to read the records (i.e. you won't write them back) you will gain a performance boost by turning of change tracking for your context:

yourDbContext.Configuration.AutoDetectChangesEnabled = false;

Do this before loading any entities. If you need to update the loaded records you can allways call

yourDbContext.ChangeTracker.DetectChanges();

before calling SaveChanges().

回答3:

The moment I hear statements like: "The company is standardized on EF4 or EF5, or whatever" This sends cold shivers down my spine.

It is the equivalent of a car rental saying "We have standardized on a single car model for our entire fleet".

Or a carpenter saying "I have standardized on chisels as my entire toolkit. I will not have saws, drills etc..."

There is something called the right tool for the right job This statement only highlights that the person in charge of making key software architecture decisions has no clue about software architecture.

If you are dealing with over 100K records and the datamodels are complex (i.e. non trivial), Maybe EF6 is not the best option. EF6 is based on the concepts of dynamic reflection and has similar design patterns to Castle Project Active Record

Do you need to load all of the 100K records into memory and perform operations on these ? If yes ask yourself do you really need to do that and why wouldn't executing a stored procedure across the 100K records achieve the same thing. Do some analysis and see what is the actual data usage pattern. Maybe the user performs a search which returns 100K records but they only navigate through the first 200. Example google search, Hardly anyone goes past page 3 of the millions of search results.

If the answer is still yes you need to load all of the 100K records into memory and perform operations. Then maybe you need to consider something else like a custom built write through cache with light weight objects. Maybe lazy load dynamic object pointers for nested objects. etc... One instance where I use something like this is large product catalogs for eCommerce sites where very large numbers of searches get executed against the catalog. Why is in order to provide custom behavior such as early exit search, and regex wildcard search using pre-compiled regex, or custom Hashtable indexes into the product catalog.

There is no one size fits all answer to this question. It all depends the data usage scenarios and how the application works with the data. Consider Gorilla Vs Shark who would win? It all depends on the environment and the context.

Maybe EF6 is perfect for one piece that would benefit from dynamic reflection, While NetTiers is better for another that needs static reflection and an extensible ORM. While low level ADO is perhaps best for extreme high performance pieces.