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Overview
Comment:Minor change to wal.c on this branch to make it more similar to trunk.
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SHA3-256: 6a7af3ead5949c461430c1fa92798dc2bbbc58c8cd504005c5afa38993f0be82
User & Date: dan 2018-12-03 20:38:15
Wiki:begin-concurrent
Context
2018-12-04
13:51
Fix a problem with SQLITE_ENABLE_EXPENSIVE_ASSERT builds on this branch. check-in: ddb4a6fb user: dan tags: begin-concurrent
2018-12-03
20:49
Merge the wal2 and begin-concurrent code. Both features work, but not at the same time. check-in: b7281a1c user: dan tags: begin-concurrent-wal2
20:38
Minor change to wal.c on this branch to make it more similar to trunk. check-in: 6a7af3ea user: dan tags: begin-concurrent
19:29
Cherrypick a couple of fixes from begin-concurrent-pnu into this branch. The differences between the two branches are now that this one does not have "PRAGMA noop_update" or the mutex-free PRNG. check-in: a56506b9 user: dan tags: begin-concurrent
Changes
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Changes to src/wal.c.

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  if( pWal->readLock>=0 ){
    walUnlockShared(pWal, WAL_READ_LOCK(pWal->readLock));
    pWal->readLock = -1;
  }
}

/*
** Search the hash tables for an entry matching page number pgno. Ignore
** any entries that lie after frame iLast within the wal file.




*/
static int walFindFrame(
  Wal *pWal, 
  Pgno pgno, 
  u32 iLast, 
  u32 *piRead



){


  int iHash;                      /* Used to loop through N hash tables */
  u32 iRead = 0;
  int iMinHash;















  /* Each iteration of the following for() loop searches one
  ** hash table (each hash table indexes up to HASHTABLE_NPAGE frames).
  **
  ** This code might run concurrently to the code in walIndexAppend()
  ** that adds entries to the wal-index (and possibly to this hash 
  ** table). This means the value just read from the hash 
................................................................................
      if( (nCollide--)==0 ){
        return SQLITE_CORRUPT_BKPT;
      }
    }
    if( iRead ) break;
  }

  *piRead = iRead;
  return SQLITE_OK;
}

/*
** Search the wal file for page pgno. If found, set *piRead to the frame that
** contains the page. Otherwise, if pgno is not in the wal file, set *piRead
** to zero.
**
** Return SQLITE_OK if successful, or an error code if an error occurs. If an
** error does occur, the final value of *piRead is undefined.
*/
int sqlite3WalFindFrame(
  Wal *pWal,                      /* WAL handle */
  Pgno pgno,                      /* Database page number to read data for */
  u32 *piRead                     /* OUT: Frame number (or zero) */
){
  u32 iRead = 0;                  /* If !=0, WAL frame to return data from */
  u32 iLast = pWal->hdr.mxFrame;  /* Last page in WAL for this reader */
  int rc;

  /* This routine is only be called from within a read transaction. */
  assert( pWal->readLock>=0 || pWal->lockError );

  /* If the "last page" field of the wal-index header snapshot is 0, then
  ** no data will be read from the wal under any circumstances. Return early
  ** in this case as an optimization.  Likewise, if pWal->readLock==0, 
  ** then the WAL is ignored by the reader so return early, as if the 
  ** WAL were empty.
  */
  if( iLast==0 || (pWal->readLock==0 && pWal->bShmUnreliable==0) ){
    *piRead = 0;
    return SQLITE_OK;
  }

  rc = walFindFrame(pWal, pgno, iLast, &iRead);

#ifdef SQLITE_ENABLE_EXPENSIVE_ASSERT
  /* If expensive assert() statements are available, do a linear search
  ** of the wal-index file content. Make sure the results agree with the
  ** result obtained using the hash indexes above.  */
  if( rc==SQLITE_OK ){
    u32 iRead2 = 0;
    u32 iTest;
................................................................................
      }
    }
    assert( iRead==iRead2 );
  }
#endif

  *piRead = iRead;
  return rc;
}

/*
** Read the contents of frame iRead from the wal file into buffer pOut
** (which is nOut bytes in size). Return SQLITE_OK if successful, or an
** error code otherwise.
*/







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  if( pWal->readLock>=0 ){
    walUnlockShared(pWal, WAL_READ_LOCK(pWal->readLock));
    pWal->readLock = -1;
  }
}

/*
** Search the wal file for page pgno. If found, set *piRead to the frame that
** contains the page. Otherwise, if pgno is not in the wal file, set *piRead
** to zero.
**
** Return SQLITE_OK if successful, or an error code if an error occurs. If an
** error does occur, the final value of *piRead is undefined.
*/
int sqlite3WalFindFrame(




  Wal *pWal,                      /* WAL handle */
  Pgno pgno,                      /* Database page number to read data for */
  u32 *piRead                     /* OUT: Frame number (or zero) */
){
  u32 iRead = 0;                  /* If !=0, WAL frame to return data from */
  u32 iLast = pWal->hdr.mxFrame;  /* Last page in WAL for this reader */
  int iHash;                      /* Used to loop through N hash tables */

  int iMinHash;

  /* This routine is only be called from within a read transaction. */
  assert( pWal->readLock>=0 || pWal->lockError );

  /* If the "last page" field of the wal-index header snapshot is 0, then
  ** no data will be read from the wal under any circumstances. Return early
  ** in this case as an optimization.  Likewise, if pWal->readLock==0, 
  ** then the WAL is ignored by the reader so return early, as if the 
  ** WAL were empty.
  */
  if( iLast==0 || (pWal->readLock==0 && pWal->bShmUnreliable==0) ){
    *piRead = 0;
    return SQLITE_OK;
  }

  /* Each iteration of the following for() loop searches one
  ** hash table (each hash table indexes up to HASHTABLE_NPAGE frames).
  **
  ** This code might run concurrently to the code in walIndexAppend()
  ** that adds entries to the wal-index (and possibly to this hash 
  ** table). This means the value just read from the hash 
................................................................................
      if( (nCollide--)==0 ){
        return SQLITE_CORRUPT_BKPT;
      }
    }
    if( iRead ) break;
  }






































#ifdef SQLITE_ENABLE_EXPENSIVE_ASSERT
  /* If expensive assert() statements are available, do a linear search
  ** of the wal-index file content. Make sure the results agree with the
  ** result obtained using the hash indexes above.  */
  if( rc==SQLITE_OK ){
    u32 iRead2 = 0;
    u32 iTest;
................................................................................
      }
    }
    assert( iRead==iRead2 );
  }
#endif

  *piRead = iRead;
  return SQLITE_OK;
}

/*
** Read the contents of frame iRead from the wal file into buffer pOut
** (which is nOut bytes in size). Return SQLITE_OK if successful, or an
** error code otherwise.
*/