Slowness in testing any crossing straight lines in a layer

[Bo Guo]

Hi There!

I have 100K straight lines in a layer - my_fishbone -  with GIST indexed.
However, the following SQL query did not finish within 20 minutes!  Could
you advise on any improvement ideas?

SELECT a.*, b.id
FROM my_fishbones a, my_fishbones b
WHERE a.geom && b.geom
  AND ST_Crosses(a.geom, b.geom)

Thanks in advance!

Bo Guo