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[TEST] sqlite3-3.7.17-3

This is the first formal test release of SQLite 3.7.17. These are -3 packages because there were two informal test releases prior to this.

Because it is a "test" release, you have to select it specially from the setup.exe packages screen. You still get by default.

Aside from tracking the upstream .17 release, this Cygwin build does many things, which is why I am going through a multistage test sequence. This is the last stage before final release.

Heretofore, Cygwin SQLite has been built in "Cygwin mode," where SQLite bypasses the Cygwin DLL for some calls, particularly in regards to file locking. These calls go straight to the Win32 API. This lets Cygwin SQLite do file locking the same way native Win32 builds of SQLite do, so that any pair of programs can cooperate in their use of a single DB file, regardless of which version of SQLite they are built against.

I did once ( ship Cygwin SQLite built the other way, in "Unix mode," which forces the SQLite code to treat Cygwin as any other POSIX platform. This has the benefit that file locking works the way POSIX programs expect, but it breaks compatibility with the huge number of programs built against native SQLite.

This gave me a choice of evils: I could choose to break compatibility with native Win32 programs, or I could break compatibility with other Cygwin programs. I chose the second option, simply because there are more native Win32 programs than Cygwin programs using SQLite.

This impasse was broken -- we hope -- by a feature added by Corinna in Cygwin 1.7.19 and extended in 1.7.20. It allows a program -- such as Cygwin SQLite -- to request that the DLL do file locking in a way more compatible with native Windows programs. This release uses this new feature by default, so that despite being built in Unix mode, it should still interoperate with native Windows programs that also use SQLite.

You do require Cygwin 1.7.20 to properly test this new package. The variant of the feature in 1.7.19 doesn't work for SQLite, so this -3 test release no longer has code to attempt to enable it. (The original version of this new feature may still be useful to other programs, so it hasn't been removed from the Cygwin DLL.) These new packages will still run under Cygwin 1.7.18 and earlier, but they will behave the same as the ill-fated SQLite release in regards to locking.

If you have had problems in the past with SQLite interoperability with native Windows programs, please test with this new release. You shouldn't have to do anything to test its interoperability with native Windows programs.

If your interop problems were with other Cygwin programs, then you want to set the new CYGWIN_SQLITE_LOCKING environment variable to "posix". (Case doesn't matter.) This will suppress Cygwin SQLite's call to the new Cygwin API, so it behaves like a stock Unix mode build.

Because this test release removes the "posixmand" feature, if you tested the -1 or -2 releases, I ask that you re-test with -3. I believe you will see no change, but y'all are the ones with all the important test cases. :)

This version of Cygwin SQLite also makes one other big, potentially breaking change: temporary files are created in-memory exclusively, by default.

There is some concern that this could cause problems with huge DB files on 32-bit Cygwin. If this version of SQLite fails with some out-of-memory error with your DB, there is a pragma you can set to make it behave the old way:

If setting this pragma to 1 fixes such an error, I want to hear it! (I'd also be curious to know how big the DB file is, and how much RAM there is in your machine.)

Note that this isn't the same thing as loading the entire DB into RAM. If your DB is, say, 5 GB, you needn't worry about 4 GB memory limits in 32-bit systems. The problem should only come up with DB files much bigger than this, so that it needs gigs just to store its temporary working data.

The open question is what that ratio is, between DB file size and working set size. It is doubtless dependent on the queries you run, and probably on other things like indexing.

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