Performance features

If your program's database interaction is not as efficient as it needs to be, the first place to look is usually the SQL you're executing. But libpqxx has a few specialized features to help you squeeze more performance out of how you issue commands and retrieve data:

- Streams. Use these as a faster way to transfer data between your code and the database.
- `std::string_view` and `pqxx::zview`. In places where traditional C++ worked with `std::string`, see whether `std::string_view` or `pqxx::zview` will do. Of course that means that you'll have to look at the data's lifetime more carefully, but it'll save the computer a lot of copying.
- Prepared statements. These can be executed many times without the server parsing and planning them anew each time. They also save you having to escape string parameters.
- `pqxx::pipeline` lets you send queries to the database in batches, and continue other processing while they are executing.
- `pqxx::connecting` lets you start setting up a database connection, but without blocking the thread.

As always of course, don't risk the quality of your code for optimizations that you don't need!