Index files are not used in the session where they were created

I'm investigating whether index-caches help with slow symbols
loading (https://sourceware.org/bugzilla/show_bug.cgi?id=30520).

They seem to help, but only on the second gdb run. When I start a
debug session for the first time with an empty ~/.caches/gdb
directory, I can see from logs that gdb tries to read index
files, fails because they don't exist, and then writes index to
disk. The index is saved in a few seconds.

If I then try loading children of a variable causing a slow symbol
lookup, the lookup is still slow. Even though the index is ready
and is saved to disk.

If I restart gdb after the index is written, then gdb picks it
up, and symbol loading is much faster - a few seconds instead of
a minute.

Is there a way to use the created index without gdb restart?

-- 
Dmitrii Neverov