text search too slow on sqlite db on tableview on iphone

Question

I have a large table of around 2500 entries. I am displaying it on tableview. however the search bar is too slow while doing dynamic search. ie I am filtering the table ever

Answer 1

SQLite's selects are usually very fast. If you posted some sample queries, it'd probably be easier to help you.

However, that said: If you have a query with a simple WHERE clause that's performing slowly, you probably don't have an index on the column that's being searched. Add one.

2500 entries in a table is NOT large for SQLite. 25,000,000 would be large.

When you're working with SQLite, you can test a lot of things on the desktop using the sqlite3 shell. For instance, if your query is something like:

SELECT * FROM MyTable WHERE Column='A';

You can do something like this:

EXPLAIN QUERY PLAN SELECT * FROM MyTable WHERE Column='A';

If you see output like this:

0|0|TABLE MyTable

It means SQLite is crawling the entire table to get the results.

In this case, adding an index would help:

CREATE INDEX MyTableColumn ON MyTable(Column);

Then, the explain above will give you something like this instead:

0|0|TABLE MyTable WITH INDEX MyTableColumn

If your WHERE clause is more complicated, you might need to make a compound index instead, since SQLite will only use one index per table.

CREATE INDEX MyTableFirstSecond ON MyTable(First,Second);

So in your case:

1. Get your database onto the Mac.
2. Use the shell to diagnose which of your queries are slow.
3. Study the queries to see why they're slow: What needs to be indexed? And less likely: What about the query is awkward, preventing the query optimizer from picking a sensible plan?
4. Add the appropriate indexes or tune the query.
5. Re-test to make sure the change works.

The rule of thumb with SQLite is simple: If you're going to search on it, it should be indexed.

Answer 2

After the first character, copy the resulting data into an array and then filter the array using a predicate. It's much faster. Then reload your table from the array. The array might be an array of dictionaries where each element is a dictionary with the search string (i.e. name or whatever) and the other entry is a reference to the core data entity that you want as the final selection. Or you can just so the core data selection at the end when the user makes a selection.

Note that when you filter with a predicate, the objects in the array need to have properties that match what you are searching for. In my example, I created an object that had properties fullName emailAddressString etc..

predicate = [NSPredicate predicateWithFormat:@"fullName contains[cd] %@ or emailAddressString contains[cd] %@", searchString, searchString];

NSArray *resultArray = [[NSArray alloc] initWithArray:[allContacts filteredArrayUsingPredicate:predicate]];