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Fix a comment in btree.c (CVS 3702)

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FossilOrigin-Name: 05700c11a9e5177a437d2240e72fb61ea47b973b
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drh
2007-03-19 11:54:10 +00:00
parent 4099f6e129
commit fe5d71dd7f
3 changed files with 14 additions and 23 deletions
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21
src/btree.c
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@@ -9,7 +9,7 @@
** May you share freely, never taking more than you give.
**
*************************************************************************
** $Id: btree.c,v 1.339 2007/03/19 11:25:20 danielk1977 Exp $
** $Id: btree.c,v 1.340 2007/03/19 11:54:10 drh Exp $
**
** This file implements a external (disk-based) database using BTrees.
** For a detailed discussion of BTrees, refer to
@@ -2649,25 +2649,16 @@ static int dfltCompare(
**
** 1: The cursor must have been opened with wrFlag==1
**
** 2: No other cursors may be open with wrFlag==0 on the same table
** 2: Other database connections that share the same pager cache
** but which are not in the READ_UNCOMMITTED state may not have
** cursors open with wrFlag==0 on the same table. Otherwise
** the changes made by this write cursor would be visible to
** the read cursors in the other database connection.
**
** 3: The database must be writable (not on read-only media)
**
** 4: There must be an active transaction.
**
** Condition 2 warrants further discussion. If any cursor is opened
** on a table with wrFlag==0, that prevents all other cursors from
** writing to that table. This is a kind of "read-lock". When a cursor
** is opened with wrFlag==0 it is guaranteed that the table will not
** change as long as the cursor is open. This allows the cursor to
** do a sequential scan of the table without having to worry about
** entries being inserted or deleted during the scan. Cursors should
** be opened with wrFlag==0 only if this read-lock property is needed.
** That is to say, cursors should be opened with wrFlag==0 only if they
** intend to use the sqlite3BtreeNext() system call. All other cursors
** should be opened with wrFlag==1 even if they never really intend
** to write.
**
** No checking is done to make sure that page iTable really is the
** root page of a b-tree. If it is not, then the cursor acquired
** will not work correctly.