Enhanced comments on table locking logic as it relates to preparing new
statements. Added assert() and testcase() but no other changes to code. (CVS 6319) FossilOrigin-Name: 4a12f5b818b769d7518c942ff3dedf453dde698e
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drh
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16
manifest
@ -1,5 +1,5 @@
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C Add\stest\sfile\stest/count.test\sfor\stesting\s"SELECT\scount(*)"\sstatements.\sIt\sis\snot\sproperly\spopulated\syet.\s(CVS\s6318)
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D 2009-02-24T10:48:28
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C Enhanced\scomments\son\stable\slocking\slogic\sas\sit\srelates\sto\spreparing\snew\nstatements.\s\sAdded\sassert()\sand\stestcase()\sbut\sno\sother\schanges\sto\scode.\s(CVS\s6319)
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D 2009-02-24T16:18:05
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F Makefile.arm-wince-mingw32ce-gcc fcd5e9cd67fe88836360bb4f9ef4cb7f8e2fb5a0
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F Makefile.in d64baddbf55cdf33ff030e14da837324711a4ef7
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F Makefile.linux-gcc d53183f4aa6a9192d249731c90dbdffbd2c68654
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@ -103,7 +103,7 @@ F src/auth.c c8b2ab5c8bad4bd90ed7c294694f48269162c627
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F src/backup.c 2d3f31148d7b086c5c72d9edcd04fc2751b0aa6e
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F src/bitvec.c 44f7059ac1f874d364b34af31b9617e52223ba75
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F src/btmutex.c 63c5cc4ad5715690767ffcb741e185d7bc35ec1a
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F src/btree.c e0178d6fb69c8f332f3fba96cfc0b08275ad5e76
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F src/btree.c 8b8697ab5e8ca9aad12221bb9abfee1aed7a5cd1
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F src/btree.h 96a019c9f28da38e79940512d7800e419cd8c702
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F src/btreeInt.h 0a4884e6152d7cae9c741e91b830064c19fd2c05
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F src/build.c a1db48aec62c95049d783f231195812ff97ae268
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@ -149,7 +149,7 @@ F src/pcache.c fcf7738c83c4d3e9d45836b2334c8a368cc41274
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F src/pcache.h 9b927ccc5a538e31b4c3bc7eec4f976db42a1324
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F src/pcache1.c dabb8ab14827e090321f17150ce96fda172974e8
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F src/pragma.c 22ed04836aab8ce134c53be1ca896f3ad20fabdb
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F src/prepare.c d0bbb4b1a8b9c1db6d13788929839bb63764680e
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F src/prepare.c 1ede93a00f1835a10b3d3aad968e8f8ecd2c98dd
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F src/printf.c 9866a9a9c4a90f6d4147407f373df3fd5d5f9b6f
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F src/random.c 676b9d7ac820fe81e6fb2394ac8c10cff7f38628
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F src/resolve.c dea005135845acbbfae1f2968c0deb6b2e3d580c
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@ -702,7 +702,7 @@ F tool/speedtest16.c c8a9c793df96db7e4933f0852abb7a03d48f2e81
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F tool/speedtest2.tcl ee2149167303ba8e95af97873c575c3e0fab58ff
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F tool/speedtest8.c 2902c46588c40b55661e471d7a86e4dd71a18224
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F tool/speedtest8inst1.c 293327bc76823f473684d589a8160bde1f52c14e
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P 0e7c369c23a8767b4d3e5cdd47c14716992fb71a
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R 71f287412eb030dfd9b14d26e52b17fb
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U danielk1977
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Z e2d5b34166a5d213f9445c572c8e416e
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P a195d74ff9ce836447dba4da7edcc6f1cdae5574
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R 7311b1fa9b7b5c3d12ba433576f5510b
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U drh
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Z 99368cf9c56a6d99659a698dff53e252
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@ -1 +1 @@
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a195d74ff9ce836447dba4da7edcc6f1cdae5574
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4a12f5b818b769d7518c942ff3dedf453dde698e
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18
src/btree.c
18
src/btree.c
@ -9,7 +9,7 @@
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** May you share freely, never taking more than you give.
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**
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*************************************************************************
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** $Id: btree.c,v 1.567 2009/02/24 10:01:52 danielk1977 Exp $
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** $Id: btree.c,v 1.568 2009/02/24 16:18:05 drh Exp $
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**
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** This file implements a external (disk-based) database using BTrees.
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** See the header comment on "btreeInt.h" for additional information.
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@ -113,8 +113,9 @@ static int queryTableLock(Btree *p, Pgno iTab, u8 eLock){
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}
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/* This (along with lockTable()) is where the ReadUncommitted flag is
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** dealt with. If the caller is querying for a read-lock and the flag is
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** set, it is unconditionally granted - even if there are write-locks
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** dealt with. If the caller is querying for a read-lock on any table
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** other than the sqlite_master table (table 1) and if the ReadUncommitted
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** flag is set, then the lock granted even if there are write-locks
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** on the table. If a write-lock is requested, the ReadUncommitted flag
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** is not considered.
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**
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@ -122,9 +123,9 @@ static int queryTableLock(Btree *p, Pgno iTab, u8 eLock){
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** ReadUncommitted flag is set, no entry is added to the locks list
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** (BtShared.pLock).
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**
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** To summarize: If the ReadUncommitted flag is set, then read cursors do
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** not create or respect table locks. The locking procedure for a
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** write-cursor does not change.
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** To summarize: If the ReadUncommitted flag is set, then read cursors
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** on non-schema tables do not create or respect table locks. The locking
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** procedure for a write-cursor does not change.
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*/
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if(
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0==(p->db->flags&SQLITE_ReadUncommitted) ||
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@ -167,8 +168,9 @@ static int lockTable(Btree *p, Pgno iTable, u8 eLock){
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assert( SQLITE_OK==queryTableLock(p, iTable, eLock) );
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/* If the read-uncommitted flag is set and a read-lock is requested,
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** return early without adding an entry to the BtShared.pLock list. See
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/* If the read-uncommitted flag is set and a read-lock is requested on
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** a non-schema table, then the lock is always granted. Return early
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** without adding an entry to the BtShared.pLock list. See
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** comment in function queryTableLock() for more info on handling
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** the ReadUncommitted flag.
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*/
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@ -13,7 +13,7 @@
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** interface, and routines that contribute to loading the database schema
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** from disk.
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**
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** $Id: prepare.c,v 1.106 2009/02/19 14:39:25 danielk1977 Exp $
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** $Id: prepare.c,v 1.107 2009/02/24 16:18:05 drh Exp $
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*/
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#include "sqliteInt.h"
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@ -540,17 +540,39 @@ static int sqlite3Prepare(
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assert( !db->mallocFailed );
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assert( sqlite3_mutex_held(db->mutex) );
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/* If any attached database schemas are locked, do not proceed with
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** compilation. Instead return SQLITE_LOCKED immediately.
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/* Check to verify that it is possible to get a read lock on all
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** database schemas. The inability to get a read lock indicates that
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** some other database connection is holding a write-lock, which in
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** turn means that the other connection has made uncommitted changes
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** to the schema.
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**
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** Were we to proceed and prepare the statement against the uncommitted
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** schema changes and if those schema changes are subsequently rolled
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** back and different changes are made in their place, then when this
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** prepared statement goes to run the schema cookie would fail to detect
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** the schema change. Disaster would follow.
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**
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** This thread is currently holding mutexes on all Btrees (because
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** of the sqlite3BtreeEnterAll() in sqlite3LockAndPrepare()) so it
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** is not possible for another thread to start a new schema change
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** while this routine is running. Hence, we do not need to hold
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** locks on the schema, we just need to make sure nobody else is
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** holding them.
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**
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** Note that setting READ_UNCOMMITTED overrides most lock detection,
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** but it does *not* override schema lock detection, so this all still
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** works even if READ_UNCOMMITTED is set.
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*/
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for(i=0; i<db->nDb; i++) {
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Btree *pBt = db->aDb[i].pBt;
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if( pBt ){
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assert( sqlite3BtreeHoldsMutex(pBt) );
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rc = sqlite3BtreeSchemaLocked(pBt);
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if( rc ){
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const char *zDb = db->aDb[i].zName;
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sqlite3Error(db, SQLITE_LOCKED, "database schema is locked: %s", zDb);
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(void)sqlite3SafetyOff(db);
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testcase( db->flags & SQLITE_ReadUncommitted );
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return sqlite3ApiExit(db, SQLITE_LOCKED);
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}
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}
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