• Tom Lane's avatar
    Allow extensions to generate lossy index conditions. · 74dfe58a
    Tom Lane authored
    For a long time, indxpath.c has had the ability to extract derived (lossy)
    index conditions from certain operators such as LIKE.  For just as long,
    it's been obvious that we really ought to make that capability available
    to extensions.  This commit finally accomplishes that, by adding another
    API for planner support functions that lets them create derived index
    conditions for their functions.  As proof of concept, the hardwired
    "special index operator" code formerly present in indxpath.c is pushed
    out to planner support functions attached to LIKE and other relevant
    operators.
    
    A weak spot in this design is that an extension needs to know OIDs for
    the operators, datatypes, and opfamilies involved in the transformation
    it wants to make.  The core-code prototypes use hard-wired OID references
    but extensions don't have that option for their own operators etc.  It's
    usually possible to look up the required info, but that may be slow and
    inconvenient.  However, improving that situation is a separate task.
    
    I want to do some additional refactorization around selfuncs.c, but
    that also seems like a separate task.
    
    Discussion: https://postgr.es/m/15193.1548028093@sss.pgh.pa.us
    74dfe58a
supportnodes.h 11.1 KB