Hi there!
I'm trying to implement a custom indexing system using the GiST index framework, and I have a few questions.
Basically, I'm trying to implement a system that allows me to search across a set of 64 bit integers by hamming distance. This is intended to be used in searching for similar images, where the 64 bit integer is actually a
phash of an image, and similarity between two images is reflected in the hamming distance between two integers.
Anyways, The appropriate approach here is to use something called a
BK tree, for which I've
written some test code and I think I have a decent grip of (my test code seems to work, in any event).
That said:
- Is there a simple piece of example-code for implementing a GiST index for a single index? I've been looking through the /contrib/ directory, particularly the /contrib/btree_gist/ files, but it looks like 90% of the complexity there is related to supporting all the column types Postgres has, rather then actually tied to producing a functional index.
- Once I have something compiling, how can I check to be sure that I'm actually using the indexing module I created? I can enable my compiled extension using `CREATE EXTENSION`, but is there an option for `CREATE INDEX test_index ON testing USING gist (val);` that lets me specify *which* GiST index is actually employed? Is this even a valid question?
This is probably something that's available in one of the system tables somewhere, but I haven't had much luck with google finding out where. - Testing: What's the appropriate way to examine the generated tree structure of the index? I certainly went through a few bugs with my test tree system (and that was in python!). Is there any way to examine the index structure for debugging purposes?
- Also, it looks like `ereport()` is the proper way to emit debugging information. Is this correct?
- In that vein, is there any way to have information that is on the operations of an entire query? Looking at the number of tree nodes touched for a scan would be nice (and I would not be surprised if there is already a facility for it).
Project code is here if anyone is interested, any help would be great. I have very little idea what I'm doing.
Thanks,
Connor