/*
** Allocate a new database file block to write data to, either by extending
** the database file or by recycling a free-list entry. The worker snapshot
** must be held in order to call this function.
**
** If successful, *piBlk is set to the block number allocated and LSM_OK is
** returned. Otherwise, *piBlk is zeroed and an lsm error code returned.
*/
int lsmBlockAllocate(lsm_db *pDb, int *piBlk){
Database *p = pDb->pDatabase;
Snapshot *pWorker; /* Worker snapshot */
Freelist *pFree; /* Database free list */
int iRet = 0; /* Block number of allocated block */
pWorker = pDb->pWorker;
pFree = &pWorker->freelist;
if( pFree->nEntry>0 ){
/* The first block on the free list was freed as part of the work done
** to create the snapshot with id iFree. So, we can reuse this block if
** snapshot iFree or later has been checkpointed and all currently
** active clients are reading from snapshot iFree or later.
*/
Snapshot *pIter;
i64 iFree = pFree->aEntry[0].iId;
i64 iInUse;
/* Both Database.iCheckpointId and the Database.pClient list are
** protected by the client mutex. So grab it here before determining
** the id of the oldest snapshot still potentially in use. */
lsmMutexEnter(pDb->pEnv, p->pClientMutex);
assertSnapshotListOk(p);
for(pIter=p->pClient; pIter->pSnapshotNext; pIter=pIter->pSnapshotNext);
iInUse = LSM_MIN(pIter->iId, p->iCheckpointId);
lsmMutexLeave(pDb->pEnv, p->pClientMutex);
if( iFree<=iInUse ){
iRet = pFree->aEntry[0].iBlk;
flRemoveEntry0(pFree);
assert( iRet!=0 );
if( pWorker->bRecordDelta ){
pWorker->aDelta[0]++;
}
}
}
/* If no block was allocated from the free-list, allocate one at the
** end of the file. */
if( iRet==0 ){
pWorker->nBlock++;
iRet = pWorker->nBlock;
}
*piBlk = iRet;
return LSM_OK;
}
/*
** The default key-compare function.
*/
static int xCmp(void *p1, int n1, void *p2, int n2){
int res;
res = memcmp(p1, p2, LSM_MIN(n1, n2));
if( res==0 ) res = (n1-n2);
return res;
}
