One of my friends, Francesco Reinerio, with KDE, has a software called baloo that was flooding /var/log/messages with thousand of these lines:
org.kde.baloo.engine: PositionDB::put MDB_BAD_TXN: Transaction must abort, has a child, or is invalid
Solved cleaning its damn indexes:
rm -rf ~/.local/share/baloo
I want to share this experience because it was really nasty. The log was 20G.
It was not so immediate to troubleshoot because we didn't know anything about baloo internals.
Reference: