// was:balance
private RC Balance()
{
var rc = RC.OK;
var nMin = (int)this.Shared.UsableSize * 2 / 3;
var balance_quick_called = 0;
var balance_deeper_called = 0;
do
{
var pageID = this.PageID;
var page = this.Pages[pageID];
if (pageID == 0)
{
if (page.NOverflows != 0)
{
// The root page of the b-tree is overfull. In this case call the balance_deeper() function to create a new child for the root-page
// and copy the current contents of the root-page to it. The next iteration of the do-loop will balance the child page.
Debug.Assert((balance_deeper_called++) == 0);
rc = MemPage.balance_deeper(page, ref this.Pages[1]);
if (rc == RC.OK)
{
this.PageID = 1;
this.PagesIndexs[0] = 0;
this.PagesIndexs[1] = 0;
Debug.Assert(this.Pages[1].NOverflows != 0);
}
}
else
{
break;
}
}
else if (page.NOverflows == 0 && page.FreeBytes <= nMin)
{
break;
}
else
{
var pParent = this.Pages[pageID - 1];
var iIdx = this.PagesIndexs[pageID - 1];
rc = Pager.Write(pParent.DbPage);
if (rc == RC.OK)
{
#if !SQLITE_OMIT_QUICKBALANCE
if (page.HasData != 0 && page.NOverflows == 1 && page.Overflows[0].Index == page.Cells && pParent.ID != 1 && pParent.Cells == iIdx)
{
// Call balance_quick() to create a new sibling of pPage on which to store the overflow cell. balance_quick() inserts a new cell
// into pParent, which may cause pParent overflow. If this happens, the next interation of the do-loop will balance pParent
// use either balance_nonroot() or balance_deeper(). Until this happens, the overflow cell is stored in the aBalanceQuickSpace[]
// buffer.
// The purpose of the following Debug.Assert() is to check that only a single call to balance_quick() is made for each call to this
// function. If this were not verified, a subtle bug involving reuse of the aBalanceQuickSpace[] might sneak in.
Debug.Assert((balance_quick_called++) == 0);
rc = MemPage.balance_quick(pParent, page, _balanceQuickSpaces);
}
else
#endif
{
// In this case, call balance_nonroot() to redistribute cells between pPage and up to 2 of its sibling pages. This involves
// modifying the contents of pParent, which may cause pParent to become overfull or underfull. The next iteration of the do-loop
// will balance the parent page to correct this.
// If the parent page becomes overfull, the overflow cell or cells are stored in the pSpace buffer allocated immediately below.
// A subsequent iteration of the do-loop will deal with this by calling balance_nonroot() (balance_deeper() may be called first,
// but it doesn't deal with overflow cells - just moves them to a different page). Once this subsequent call to balance_nonroot()
// has completed, it is safe to release the pSpace buffer used by the previous call, as the overflow cell data will have been
// copied either into the body of a database page or into the new pSpace buffer passed to the latter call to balance_nonroot().
var pSpace = new byte[this.Shared.PageSize];// u8 pSpace = sqlite3PageMalloc( pCur.pBt.pageSize );
rc = MemPage.balance_nonroot(pParent, iIdx, null, pageID == 1 ? 1 : 0);
// The pSpace buffer will be freed after the next call to balance_nonroot(), or just before this function returns, whichever comes first.
}
}
page.NOverflows = 0;
// The next iteration of the do-loop balances the parent page.
page.releasePage();
this.PageID--;
}
} while (rc == RC.OK);
return(rc);
}