Wal index format questions

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Wal index format questions

Harmen
Hello,

thanks for the good documentation of the various database file formats. The wal
index one is a bit unclear to me in a few spots, maybe someone can help me out?
https://sqlite.org/walformat.html

2.1. The WAL-Index Header
there is a second copy of the WAL index information, but it's not specified
what to do with that information. Can it be ignored? Does it have to be
correct?

2.1.3. WAL Locks
does a read connection usually keep a read lock on WAL_READ_LOCK(0), and
switch to any of WAL_READ_LOCK(1..4) when it starts a transaction? Does that
also mean there is a maximum of 4 concurrent read-only transactions?

2.2. WAL-Index Hash Tables
I think I figured out how it works, but both explanations of the hashing
algorithm doesn't use the `aHash` field. It's either unclear or wrong :)
(e.g., in point 2., `aPgno[j%8192]!=0` should be `aHash[j%8192]!=0` if I
understand things correctly)

Thanks!
Harmen
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