# 2010 May 25 # # The author disclaims copyright to this source code. In place of # a legal notice, here is a blessing: # # May you do good and not evil. # May you find forgiveness for yourself and forgive others. # May you share freely, never taking more than you give. # #*********************************************************************** # set testdir [file dirname $argv0] source $testdir/tester.tcl source $testdir/lock_common.tcl source $testdir/wal_common.tcl ifcapable !wal {finish_test ; return } #------------------------------------------------------------------------- # This test case demonstrates a flaw in the wal-index manipulation that # existed at one point: If a process crashes mid-transaction, it may have # already added some entries to one of the hash-tables in the wal-index. # If the transaction were to be explicitly rolled back at this point, the # hash-table entries would be removed as part of the rollback. However, # if the process crashes, the transaction is implicitly rolled back and # the rogue entries remain in the hash table. # # Normally, this causes no problem - readers can tell the difference # between committed and uncommitted entries in the hash table. However, # if it happens often enough that all slots in the hash-table become # non-zero, the next process that attempts to read or write the hash # table falls into an infinite loop. # # Even if run with an SQLite version affected by the bug, this test case # only goes into an infinite loop if SQLite is compiled without SQLITE_DEBUG # defined. If SQLITE_DEBUG is defined, the program is halted by a failing # assert() before entering the infinite loop. # # walcrash2-1.1: Create a database. Commit a transaction that adds 8 frames # to the WAL (and 8 entry to the first hash-table in the # wal-index). # # walcrash2-1.2: Have an external process open a transaction, add 8 entries # to the wal-index hash-table, then crash. Repeat this 1023 # times (so that the wal-index contains 8192 entries - all # slots are non-zero). # # walcrash2-1.3: Using a new database connection, attempt to query the # database. This should cause the process to go into the # infinite loop. # do_test walcrash2-1.1 { execsql { PRAGMA page_size = 1024; PRAGMA auto_vacuum = off; PRAGMA journal_mode = WAL; PRAGMA synchronous = NORMAL; BEGIN; CREATE TABLE t1(x); CREATE TABLE t2(x); CREATE TABLE t3(x); CREATE TABLE t4(x); CREATE TABLE t5(x); CREATE TABLE t6(x); CREATE TABLE t7(x); COMMIT; } file size test.db-wal } [wal_file_size 8 1024] for {set nEntry 8} {$nEntry < 8192} {incr nEntry 8} { do_test walcrash2-1.2.[expr $nEntry/8] { set C [launch_testfixture] testfixture $C { sqlite3 db test.db db eval { PRAGMA cache_size = 15; BEGIN; INSERT INTO t1 VALUES(randomblob(900)); -- 1 row, 1 page INSERT INTO t1 SELECT * FROM t1; -- 2 rows, 3 pages INSERT INTO t1 SELECT * FROM t1; -- 4 rows, 5 pages INSERT INTO t1 SELECT * FROM t1; -- 8 rows, 9 pages INSERT INTO t1 SELECT * FROM t1; -- 16 rows, 17 pages INSERT INTO t1 SELECT * FROM t1 LIMIT 3; -- 20 rows, 20 pages } } close $C file size test.db-wal } [wal_file_size 16 1024] } do_test walcrash2-1.3 { sqlite3 db2 test.db execsql { SELECT count(*) FROM t1 } db2 } {0} catch { db2 close } finish_test