Indexing may fail for some documents, for a number of reasons: a helper program may be missing, the document may be corrupt, we may fail to uncompress a file because no file system space is available, etc.
The Recoll indexer in versions 1.21 and later does not retry failed files by default,
because some indexing failures can be quite costly (for example failing to uncompress a
big file because of insufficient disk space). Retrying will only occur if an explicit
option (-k) is set on the recollindex command line, or
if a script executed when recollindex starts up says so. The script is
defined by a configuration variable (checkneedretryindexscript), and
makes a rather lame attempt at deciding if a helper command may have been installed, by
checking if any of the common bin directories have changed.
