On 02/06/2018 11:57 PM, Deon Brewis wrote:
I’m trying to track down SQLITE corruptions that seems to corrupt our databases
in a consistent way. (Running on 3.20.1).
This isn’t related to a crash or hardware failure. The app is running and
reading and writing to the database fine, and then suddenly we start getting a
SQLITE_NOTADB errors. The first error we got was on trying to execute a ‘BEGIN
TRANSACTION’, and everything thereafter started failing.
When our database headers are fine, I see this:
00000000h: 53 51 4C 69 74 65 20 66 6F 72 6D 61 74 20 33 00 ; SQLite format 3.
00000010h: 10 00 02 02 00 40 20 20 00 00 10 9B 00 01 34 42 ; .....@ ...›..4B
On corruption #1, I see this:
00000000h: 15 03 01 00 20 01 91 21 85 44 17 2C ED BE 21 FA ; .... .‘!…D.,í¾!ú
00000010h: 9E 74 E7 EA 9A 0A 15 2C 99 B0 B7 3B C6 F0 35 FB ; žtçêš..,™°·;Æð5û
On corruption #2, I see this:
00000000h: 15 03 01 00 20 0F 1E CB B1 FF 9C 1E D0 D6 BB 22 ; .... ..˱ÿœ.ÐÖ»"
00000010h: 15 64 D3 F4 DD 38 FB DF A3 E0 47 B8 D7 F6 21 BC ; .dÓôÝ8ûߣàG¸×ö!¼
This bit pattern of “15 03 01 00” for the first 4 characters where it should be
“SQLi” is a bit too much of a coincidence to ignore or write off as disk error.
The rest of the header and file after the first 25-ish bytes or so, seem fine.
It’s just these first 25 bytes that gets corrupted. If I restore Offsets 0 to
Offsets 27 out of a “working” database, I get a usable file.
Under what circumstances would SQLITE even attempt to re-write the header
string?
Is this on UNIX?
Quite often this sort of thing occurs because some other module is
writing to a file-descriptor owned by SQLite. Usually because it closed
its own fd, then SQLite opened the db file and was assigned the same
integer fd value, then the rogue module wrote to the fd anyway. In other
words, some other module is doing:
close(fd);
write(fd, "1503010020...", 25);
and between those two calls SQLite is calling open() and is being
assigned a file-descriptor with the same integer value as fd.
Dan.
- Deon
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