There are two suggestions based on what I understood...
- Try using Joins instead of concatenate: Concatenate is useful to load chunks of data from multiple tables into one resultant when they have same Column names or almost same columns. Search for posts on differences for concatenate and joins
- If your tables are having values in a Matrix format try to convert it into straight table using CROSSTABLE and observe data size
Hope it helps
If your concatenated tables have very different fields, this issue can shows up.
A QVD is a very specialized file, containing:
1) A XML header in plain text, that describes all fields and another information (Creation Date, qvw filename that stored the qvd, the 'lineage' of your data, and so on)
2) A 'Symbol Table' which stores all different simbols that are present at your data, converted to binary and optimized
3) A indexed compressed colection of rows (one to each row of your raw data)
This 'smart' format is the key feature that leads to very impressive load time when you do an optimized load from a QVD
If you´re original tables have much more columns, this will impact step 3 what can lead to that issue you have noticed