kawasin73
commented
11 months ago VDBE
it uses OP_NewRowid to generate a new rowid.
sqlite> explain insert into example(col1, col2) values (1, 2);
addr opcode p1 p2 p3 p4 p5 comment
---- ------------- ---- ---- ---- ------------- -- -------------
0 Init 0 8 0 0 Start at 8
1 OpenWrite 0 2 0 2 0 root=2 iDb=0; example
2 Integer 1 2 0 0 r[2]=1
3 Integer 2 3 0 0 r[3]=2
4 NewRowid 0 1 0 0 r[1]=rowid
5 MakeRecord 2 2 4 0 r[4]=mkrec(r[2..3])
6 Insert 0 4 1 example 57 intkey=r[1] data=r[4]
7 Halt 0 0 0 0
8 Transaction 0 1 1 0 1 usesStmtJournal=0
9 Goto 0 1 0 0vdbe.c
/* Opcode: NewRowid P1 P2 P3 * *
** Synopsis: r[P2]=rowid
**
** Get a new integer record number (a.k.a "rowid") used as the key to a table.
** The record number is not previously used as a key in the database
** table that cursor P1 points to. The new record number is written
** written to register P2.
**
** If P3>0 then P3 is a register in the root frame of this VDBE that holds
** the largest previously generated record number. No new record numbers are
** allowed to be less than this value. When this value reaches its maximum,
** an SQLITE_FULL error is generated. The P3 register is updated with the '
** generated record number. This P3 mechanism is used to help implement the
** AUTOINCREMENT feature.
*/
case OP_NewRowid: { /* out2 */
/* The next rowid or record number (different terms for the same
** thing) is obtained in a two-step algorithm.
**
** First we attempt to find the largest existing rowid and add one
** to that. But if the largest existing rowid is already the maximum
** positive integer, we have to fall through to the second
** probabilistic algorithm
**
** The second algorithm is to select a rowid at random and see if
** it already exists in the table. If it does not exist, we have
** succeeded. If the random rowid does exist, we select a new one
** and try again, up to 100 times.
*/
if( !pC->useRandomRowid ){
rc = sqlite3BtreeLast(pC->uc.pCursor, &res);
if( rc!=SQLITE_OK ){
goto abort_due_to_error;
}
if( res ){
v = 1; /* IMP: R-61914-48074 */
}else{
assert( sqlite3BtreeCursorIsValid(pC->uc.pCursor) );
v = sqlite3BtreeIntegerKey(pC->uc.pCursor);
if( v>=MAX_ROWID ){
pC->useRandomRowid = 1;
}else{
v++; /* IMP: R-29538-34987 */
}
}
}If the table is empty, use 1 as the new rowid.
rowid collision is checked by NotExists vdbe operation.
sqlite> explain insert into example(rowid, col1, col2) values (1, 3, 4);
addr opcode p1 p2 p3 p4 p5 comment
---- ------------- ---- ---- ---- ------------- -- -------------
0 Init 0 14 0 0 Start at 14
1 OpenWrite 0 2 0 2 0 root=2 iDb=0; example
2 Integer 3 2 0 0 r[2]=3
3 Integer 4 3 0 0 r[3]=4
4 Integer 1 1 0 0 r[1]=1
5 NotNull 1 7 0 0 if r[1]!=NULL goto 7
6 NewRowid 0 1 0 0 r[1]=rowid
7 MustBeInt 1 0 0 0
8 Noop 0 0 0 0 uniqueness check for ROWID
9 NotExists 0 11 1 0 intkey=r[1]
10 Halt 2579 2 0 example.rowid 2
11 MakeRecord 2 2 4 0 r[4]=mkrec(r[2..3])
12 Insert 0 4 1 example 49 intkey=r[1] data=r[4]
13 Halt 0 0 0 0
14 Transaction 0 1 1 0 1 usesStmtJournal=0
15 Goto 0 1 0 0
As a first step, insert an entry to a table without using free pages.
without swap buffers