Heikki Linnakangas wrote:
* GIT (Grouped Index Tuple) indexes, which achieve index space savings
in btrees by having a single index tuple represent multiple heap tuples
[...]
Another issue is that we'd need to check how much of the use-case for
GIT has been taken over by HOT.
There is, however, a ton of overlap with index-only scans, and the
possibility to return keys from indexes, as you pointed out.
One use case that I think GIT would help a lot with are my
large address tables that are clustered by zip-code but
often queried by State, City, County, School District,
Police Beat, etc.
I imagine a GIT index on "state" would just occupy
a couple pages at most regardless of how large the
table gets. And likewise, even an index on City
would be orders of magnitude smaller than the existing
ones; since all records for any given city are all
on the same few disk pages.
Or am I misunderstanding how GIT works.
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