7-column composite key is not an issue per se (obviously you're using autonumber to convert the key to numeric value, don't you?). You can also try to create two separate docs, one on low level (DAILY) and one aggregated (SUMMARY) and use document chaining to go to detailed doc from summary.
To setup the document chaining you have to create a trigger with External => Open QlikView Document action and check "Transfer State" checkbox to transfer selections from aggregated document to detail document.
yes it effects on performance so to make as uniue no. in qlikview to compact memory use
autonumberhash256(Field1,Field2,Field3,Field4,Field5,Field6,Field7) as Key
Autonumber needs one expression as input and autonumberhashXXX can handle more inputs. So you'd use autonumber(Field1&Field2&Field3) which needs to calculate the concatenation of Field1,-2 and -3 first. Autonumberhash can take more inputs: autonumberhash128(Field1, Field2, Field3). More importantly the autonumberhash are likely more efficient in determining if the combined inputs have already been encountered or are encountered for the first time. So they are probably faster in calculating the unique integer.