The correct command to show the total bytes for each unique combination of page and server is index=web | stats sum (bytes) BY page server. In Splunk, the stats command is used to calculate aggregate statistics over the dataset, such as count, sum, avg, etc. When using the BY clause, it groups the results by the specified fields. The correct syntax does not include commas or the word 'AND' between the field names. Instead, it simply lists the field names separated by spaces within the BY clause.
References:The usage of the stats command with the BY clause is confirmed by examples in the Splunk Community, where it's explained that stats with a by foo bar will output one row for every unique combination of the by fields1.