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Overview
Comment:Fix an obscure problem with releasing savepoints stored in an in-memory journal that could cause subsequent savepoint rollback to fail. Problem reported by forum post d7338bf4901f1151, PoC #3. The problem appears to have been introduced at [23ca23894af352ea].
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SHA3-256: 73c2b50211d3ae26aeb89976ec7b9fcd7de9f152b283ec7d0809ad18bddc603e
User & Date: dan 2022-01-01 19:29:50
Original Comment: Fix an obscure problem with releasing savepoints stored in an in-memory journal that could cause subsequent savepoint rollback to fail.
Context
2022-01-02
17:24
Fix an obscure problem with releasing savepoints stored in an in-memory journal that could cause subsequent savepoint rollback to fail. (check-in: 3c0806e4 user: drh tags: branch-3.37)
2022-01-01
19:55
Attempt to fix a harmless compiler warning in FTS5. (check-in: 8e619c21 user: drh tags: trunk)
19:29
Fix an obscure problem with releasing savepoints stored in an in-memory journal that could cause subsequent savepoint rollback to fail. Problem reported by forum post d7338bf4901f1151, PoC #3. The problem appears to have been introduced at [23ca23894af352ea]. (check-in: 73c2b502 user: dan tags: trunk)
17:21
Remove an obsolete assert() statement that no longer does anything useful and which is not always true. Fix for PoC #1 of forum post d7338bf4901f1151. (check-in: c76a4c0b user: drh tags: trunk)
Changes
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Changes to src/memjournal.c.

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  if( size<p->endpoint.iOffset ){
    FileChunk *pIter = 0;
    if( size==0 ){
      memjrnlFreeChunks(p->pFirst);
      p->pFirst = 0;
    }else{
      i64 iOff = p->nChunkSize;
      for(pIter=p->pFirst; ALWAYS(pIter) && iOff<=size; pIter=pIter->pNext){
        iOff += p->nChunkSize;
      }
      if( ALWAYS(pIter) ){
        memjrnlFreeChunks(pIter->pNext);
        pIter->pNext = 0;
      }
    }








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  if( size<p->endpoint.iOffset ){
    FileChunk *pIter = 0;
    if( size==0 ){
      memjrnlFreeChunks(p->pFirst);
      p->pFirst = 0;
    }else{
      i64 iOff = p->nChunkSize;
      for(pIter=p->pFirst; ALWAYS(pIter) && iOff<size; pIter=pIter->pNext){
        iOff += p->nChunkSize;
      }
      if( ALWAYS(pIter) ){
        memjrnlFreeChunks(pIter->pNext);
        pIter->pNext = 0;
      }
    }
︙︙

Changes to src/pager.c.

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** sub-journal rolled back the content could not be restored and the
** database image would become corrupt. It is therefore fortunate that 
** this circumstance cannot arise.
*/
#if defined(SQLITE_DEBUG)
static void assertTruncateConstraintCb(PgHdr *pPg){
  assert( pPg->flags&PGHDR_DIRTY );
  assert( !subjRequiresPage(pPg) || pPg->pgno<=pPg->pPager->dbSize );
}
static void assertTruncateConstraint(Pager *pPager){
  sqlite3PcacheIterateDirty(pPager->pPCache, assertTruncateConstraintCb);
}
#else
# define assertTruncateConstraint(pPager)
#endif








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** sub-journal rolled back the content could not be restored and the
** database image would become corrupt. It is therefore fortunate that 
** this circumstance cannot arise.
*/
#if defined(SQLITE_DEBUG)
static void assertTruncateConstraintCb(PgHdr *pPg){
  assert( pPg->flags&PGHDR_DIRTY );
  assert( pPg->pgno<=pPg->pPager->dbSize || !subjRequiresPage(pPg) );
}
static void assertTruncateConstraint(Pager *pPager){
  sqlite3PcacheIterateDirty(pPager->pPCache, assertTruncateConstraintCb);
}
#else
# define assertTruncateConstraint(pPager)
#endif
︙︙

Added test/memjournal2.test. 































































































































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# 2022 Jan 01
#
# 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.
#
#***********************************************************************
# Tests focused on the in-memory journal.
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl
source $testdir/malloc_common.tcl
set testprefix memjournal2

do_execsql_test 1.0 {
  PRAGMA journal_mode = memory;
  CREATE TABLE t1(a INTEGER PRIMARY KEY, b UNIQUE);
} {memory}

set nRow [expr 2000]

do_execsql_test 1.1 {
  BEGIN;
    WITH s(i) AS (
      SELECT 1 UNION ALL SELECT i+1 FROM s WHERE i<$nRow
    )
    INSERT INTO t1 SELECT NULL, randomblob(700) FROM s;
}

for {set jj 200} {$jj <= 300} {incr jj} {
  do_execsql_test 1.2.$jj.1 {
    SAVEPOINT one; 
      UPDATE t1 SET b=randomblob(700) WHERE a<=$jj;
  }
  do_execsql_test 1.2.$jj.2 {
      SAVEPOINT two;
        UPDATE t1 SET b=randomblob(700) WHERE a==1;
      ROLLBACK TO two;
      RELEASE two;
  }
  do_execsql_test 1.2.$jj.3 {
      SAVEPOINT two;
        UPDATE t1 SET b=randomblob(700) WHERE a==1;
      ROLLBACK TO two;
      RELEASE two;
  }

  do_execsql_test 1.2.$jj.4 {
    PRAGMA integrity_check;
    ROLLBACK TO one;
    RELEASE one;
  } {ok}
} 


finish_test