This past week has been very nerve racking but also exciting. We have successfully compiled PostGIS under the mingw64 chain and built a PostGIS windows 64-bit for 2.0 (and 1.5), that can install under the Enterprise Db VC++ 64-bit builds of PostgreSQL 9.1. We haven't tried on 9.0, but we assume that should be fairly trivial. Note only that, but it passes most of the PostGIS battery of tests. We first want to thank a group of people which made this all possible:

• Andrew Dunstan we are greatly indebted to for making it possible to compile PostgreSQL under mingw64 tool chain. As much as people have whined about wanting to compile PostGIS under a pure VC chain, this is not possible at this juncture just because a lot of the tests and other tool chains PostGIS uses for building are too tied to the Unix build environment.
• We want to thank the generous folks who provided money for our campaign so that we could funnel time from paid consulting work to focus on this effort and to prove that every little bit counts.
• SpatiaLite developer Alessandro Furieri whose mingw64 compile instructions were invaluable to helping us overcome our GEOS and other compile obstacles. SpatiaLite (the OGC spatial extender for SQLite),uses much of the same plumbing that PostGIS uses under the hood, so many of the lessons he learned an provide could be put to use with our problems.
• To Paul Ramsey especially and other PostGIS devs for general moral support and helping us tackle some PostGIS specific issues when compiled with mingw64. Paul demonstrated that yes you can mix VC++ built components with MingW and steps on how to do it. Part of the reason for that is the newer mingw32 seemed to crash with GEOS compiled under mingw32. Though the mingw64 chain didn't have this issue once we overcame our compile obstacle. We may in the future compare and see if compiling Geos under VC++ provides better performance and will also get us closer to having it possible to compile PostGIS fully under VC++ if people choose to. For the time being having a single tool chain that we can extract and run with is most important. We are preparing a self-standing Mingw64 tool chain with all the components needed to build PostGIS already compiled so that windows users who want to help with PostGIS need only extract to have a fully functioning postGIS dev environment and we also plan to move our mingw32 build to mingw64 chain of tools.

We hope to have a 64-bit compiled download ready next week for PostGIS 2.0.0 beta3 for people to try out. We are working on some issues with the raster2pgsql and loader/dumper guis we compiled not working right, but the core PostGIS works just fine in 64-bit and the 32-bit loader tools work fine against a 64-bit install. One thing we did notice with the 64-bit PostgreSQL is that we can set shared_buffers much higher than the 32-bit PostgreSQL windows. On windows we could never go beyond ~700MB without it not being able to start or crashing. With the 64-bit we were able to go to 2GB. Haven't tried higher yet. We hope this will prove to be a performance boost for tasks such as geocoding that reuse a lot of the same datasets and benefit a lot from share memory.