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 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.
