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Enhanced comments on table locking logic as it relates to preparing new

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statements.  Added assert() and testcase() but no other changes to code. (CVS 6319)

FossilOrigin-Name: 4a12f5b818b769d7518c942ff3dedf453dde698e
This commit is contained in:
drh
2009-02-24 16:18:05 +00:00
parent 4d9c1dd262
commit c74d0b1dfc
4 changed files with 44 additions and 20 deletions
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18
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 1.567 2009/02/24 10:01:52 danielk1977 Exp $
** $Id: btree.c,v 1.568 2009/02/24 16:18:05 drh Exp $
**
** This file implements a external (disk-based) database using BTrees.
** See the header comment on "btreeInt.h" for additional information.
@@ -113,8 +113,9 @@ static int queryTableLock(Btree *p, Pgno iTab, u8 eLock){
}
/* This (along with lockTable()) is where the ReadUncommitted flag is
** dealt with. If the caller is querying for a read-lock and the flag is
** set, it is unconditionally granted - even if there are write-locks
** dealt with. If the caller is querying for a read-lock on any table
** other than the sqlite_master table (table 1) and if the ReadUncommitted
** flag is set, then the lock granted even if there are write-locks
** on the table. If a write-lock is requested, the ReadUncommitted flag
** is not considered.
**
@@ -122,9 +123,9 @@ static int queryTableLock(Btree *p, Pgno iTab, u8 eLock){
** ReadUncommitted flag is set, no entry is added to the locks list
** (BtShared.pLock).
**
** To summarize: If the ReadUncommitted flag is set, then read cursors do
** not create or respect table locks. The locking procedure for a
** write-cursor does not change.
** To summarize: If the ReadUncommitted flag is set, then read cursors
** on non-schema tables do not create or respect table locks. The locking
** procedure for a write-cursor does not change.
*/
if(
0==(p->db->flags&SQLITE_ReadUncommitted) ||
@@ -167,8 +168,9 @@ static int lockTable(Btree *p, Pgno iTable, u8 eLock){
assert( SQLITE_OK==queryTableLock(p, iTable, eLock) );
/* If the read-uncommitted flag is set and a read-lock is requested,
** return early without adding an entry to the BtShared.pLock list. See
/* If the read-uncommitted flag is set and a read-lock is requested on
** a non-schema table, then the lock is always granted. Return early
** without adding an entry to the BtShared.pLock list. See
** comment in function queryTableLock() for more info on handling
** the ReadUncommitted flag.
*/