VBA: Querying Access with Excel. Why so slow?

Question

I found this code online to query Access and input the data into excel (2003), but it is much slower than it should be:

Sub DataPull(SQLQuery, CellPaste)
Dim         


        

Answer 1

What about the following turnarounds or improvements:

1. Once opened, save the recordset as xml file (rst.saveToFile xxx) and then have Excel reopen it.
2. Once opened, put recordset data in an array (rst.getRows xxx), and copy the array on the active sheet
3. And, at any time, minimise all memory / access requirements: open the recordset as read-only, forward only, close the connection once the data is on your side, etc.

Answer 2

I would recommend you to create the Recordset explicitly rather than implicitly using the Execute method. When creating explicitly you can set its CursorType and LockType properties which have impact on performance.

From what I see, you're loading data in Excel, then closing the recordset. You don't need to update, count records, etc... So my advice would be to create a Recordset with CursorType = adOpenForwardOnly & LockType = adLockReadOnly:

...
RST.Open SQLQuery, Con, adOpenForwardOnly, adLockReadOnly
Range(CellPaste).CopyFromRecordset RST
...

Recordset Object (ADO)

Answer 3

I don't think you are comparing like-with-like.

In Access, when you view a Query's dataview what happens is:

• an existing open connection is used (and kept open);
• a recordset is partially filled with the first few rows only (and kept open);
• the partial resultset is shown in a grid dedicated to the task and optimized for the native data access method Access employs (direct use of the Access Database Engine DLLs, probably).

In your VBA code:

• a new connection is opened (then later closed and released);
• the recordset is fully populated using all rows (then later closed and released);
• the entire resultset is read into a Excel's generic UI using non-native data access components.

I think the most significant point there is that the dataview in Access doesn't fetch the entire resultset until you ask it to, usually by navigating to the last row in the resultset. ADO will always fetch all rows in the resultset.

Second most significant would be the time taken to read the fetched rows (assuming a full resultset) into the UI element and the fact Excel's isn't optimized for the job.

Opening, closing and releasing connections and recordsets should be insignificant but are still a factor.

I think you need to do some timings on each step of the process to find the bottleneck. When comparing to Access, ensure you are getting a full resultset e.g. check the number of rows returned.

Answer 4

The problem 9 times out of 10 is to do with the Cursor Type/Location you are using.

Using dynamic cursors over network connections can slow down the retrieval of data, even if the query executed very fast.

IF you want to get large amounts of data very quickly, you'll need to use CursorLocation = adUseClient on your connection. This mean's you'll only have a static local cursor, so you won't get live updated from other users.

However - if you are only reading data, you'll save ADO going back to the DB for each individual record to check for changes.

I recently changed this as I had a simple loop, populating a list item, and each loop was taking around 0.3s. Not to slow, but even on 1,000 records thats 30 seconds! Changing only the cursor location let the entire process complete in under 1 second.