internal static RC balance_nonroot(MemPage pParent, int iParentIdx, byte[] aOvflSpace, int isRoot)
{
var apOld = new MemPage[NB]; // pPage and up to two siblings
var apCopy = new MemPage[NB]; // Private copies of apOld[] pages
var apNew = new MemPage[NB + 2]; // pPage and up to NB siblings after balancing
var apDiv = new int[NB - 1]; // Divider cells in pParent
var cntNew = new int[NB + 2]; // Index in aCell[] of cell after i-th page
var szNew = new int[NB + 2]; // Combined size of cells place on i-th page
var szCell = new ushort[1]; // Local size of all cells in apCell[]
BtShared pBt; // The whole database
int nCell = 0; // Number of cells in apCell[]
int nMaxCells = 0; // Allocated size of apCell, szCell, aFrom.
int nNew = 0; // Number of pages in apNew[]
ushort leafCorrection; // 4 if pPage is a leaf. 0 if not
int leafData; // True if pPage is a leaf of a LEAFDATA tree
int usableSpace; // Bytes in pPage beyond the header
int pageFlags; // Value of pPage.aData[0]
int subtotal; // Subtotal of bytes in cells on one page
int iOvflSpace = 0; // First unused byte of aOvflSpace[]
//int szScratch; // Size of scratch memory requested
byte[][] apCell = null; // All cells begin balanced
//
pBt = pParent.Shared;
Debug.Assert(MutexEx.Held(pBt.Mutex));
Debug.Assert(Pager.IsPageWriteable(pParent.DbPage));
#if false
Btree.TRACE("BALANCE: begin page %d child of %d\n", pPage.pgno, pParent.pgno);
#endif
// At this point pParent may have at most one overflow cell. And if this overflow cell is present, it must be the cell with
// index iParentIdx. This scenario comes about when this function is called (indirectly) from sqlite3BtreeDelete().
Debug.Assert(pParent.NOverflows == 0 || pParent.NOverflows == 1);
Debug.Assert(pParent.NOverflows == 0 || pParent.Overflows[0].Index == iParentIdx);
// Find the sibling pages to balance. Also locate the cells in pParent that divide the siblings. An attempt is made to find NN siblings on
// either side of pPage. More siblings are taken from one side, however, if there are fewer than NN siblings on the other side. If pParent
// has NB or fewer children then all children of pParent are taken.
// This loop also drops the divider cells from the parent page. This way, the remainder of the function does not have to deal with any
// overflow cells in the parent page, since if any existed they will have already been removed.
int nOld; // Number of pages in apOld[]
int nxDiv; // Next divider slot in pParent.aCell[]
var i = pParent.NOverflows + pParent.Cells;
if (i < 2)
{
nxDiv = 0;
nOld = i + 1;
}
else
{
nOld = 3;
if (iParentIdx == 0)
{
nxDiv = 0;
}
else if (iParentIdx == i)
{
nxDiv = i - 2;
}
else
{
nxDiv = iParentIdx - 1;
}
i = 2;
}
var pRight = ((i + nxDiv - pParent.NOverflows) == pParent.Cells ? pParent.HeaderOffset + 8 : pParent.FindCell(i + nxDiv - pParent.NOverflows)); // Location in parent of right-sibling pointer
var pgno = (Pgno)ConvertEx.Get4(pParent.Data, pRight);
var rc = RC.OK;
while (true)
{
rc = pBt.getAndInitPage(pgno, ref apOld[i]);
if (rc != RC.OK)
{
goto balance_cleanup;
}
nMaxCells += 1 + apOld[i].Cells + apOld[i].NOverflows;
if (i-- == 0)
{
break;
}
if (i + nxDiv == pParent.Overflows[0].Index && pParent.NOverflows != 0)
{
apDiv[i] = 0;
pgno = ConvertEx.Get4(pParent.Overflows[0].Cell, apDiv[i]);
szNew[i] = pParent.cellSizePtr(apDiv[i]);
pParent.NOverflows = 0;
}
else
{
apDiv[i] = pParent.FindCell(i + nxDiv - pParent.NOverflows);
pgno = ConvertEx.Get4(pParent.Data, apDiv[i]);
szNew[i] = pParent.cellSizePtr(apDiv[i]);
// Drop the cell from the parent page. apDiv[i] still points to the cell within the parent, even though it has been dropped.
// This is safe because dropping a cell only overwrites the first four bytes of it, and this function does not need the first
// four bytes of the divider cell. So the pointer is safe to use later on.
//
// Unless SQLite is compiled in secure-delete mode. In this case, the dropCell() routine will overwrite the entire cell with zeroes.
// In this case, temporarily copy the cell into the aOvflSpace[] buffer. It will be copied out again as soon as the aSpace[] buffer
// is allocated.
//if (pBt.secureDelete)
//{
// int iOff = (int)(apDiv[i]) - (int)(pParent.aData); //SQLITE_PTR_TO_INT(apDiv[i]) - SQLITE_PTR_TO_INT(pParent.aData);
// if( (iOff+szNew[i])>(int)pBt->usableSize )
// {
// rc = SQLITE_CORRUPT_BKPT();
// Array.Clear(apOld[0].aData,0,apOld[0].aData.Length); //memset(apOld, 0, (i + 1) * sizeof(MemPage*));
// goto balance_cleanup;
// }
// else
// {
// memcpy(&aOvflSpace[iOff], apDiv[i], szNew[i]);
// apDiv[i] = &aOvflSpace[apDiv[i] - pParent.aData];
// }
//}
pParent.dropCell(i + nxDiv - pParent.NOverflows, szNew[i], ref rc);
}
}
// Make nMaxCells a multiple of 4 in order to preserve 8-byte alignment
nMaxCells = (nMaxCells + 3) & ~3;
// Allocate space for memory structures
apCell = MallocEx.sqlite3ScratchMalloc(apCell, nMaxCells);
if (szCell.Length < nMaxCells)
{
Array.Resize(ref szCell, nMaxCells);
}
// Load pointers to all cells on sibling pages and the divider cells into the local apCell[] array. Make copies of the divider cells
// into space obtained from aSpace1[] and remove the the divider Cells from pParent.
// If the siblings are on leaf pages, then the child pointers of the divider cells are stripped from the cells before they are copied
// into aSpace1[]. In this way, all cells in apCell[] are without child pointers. If siblings are not leaves, then all cell in
// apCell[] include child pointers. Either way, all cells in apCell[] are alike.
// leafCorrection: 4 if pPage is a leaf. 0 if pPage is not a leaf.
// leafData: 1 if pPage holds key+data and pParent holds only keys.
leafCorrection = (ushort)(apOld[0].Leaf * 4);
leafData = apOld[0].HasData;
int j;
for (i = 0; i < nOld; i++)
{
// Before doing anything else, take a copy of the i'th original sibling The rest of this function will use data from the copies rather
// that the original pages since the original pages will be in the process of being overwritten.
var pOld = apCopy[i] = apOld[i].Clone();
var limit = pOld.Cells + pOld.NOverflows;
if (pOld.NOverflows > 0 || true)
{
for (j = 0; j < limit; j++)
{
Debug.Assert(nCell < nMaxCells);
var iFOFC = pOld.FindOverflowCell(j);
szCell[nCell] = pOld.cellSizePtr(iFOFC);
// Copy the Data Locally
if (apCell[nCell] == null)
{
apCell[nCell] = new byte[szCell[nCell]];
}
else if (apCell[nCell].Length < szCell[nCell])
{
Array.Resize(ref apCell[nCell], szCell[nCell]);
}
if (iFOFC < 0) // Overflow Cell
{
Buffer.BlockCopy(pOld.Overflows[-(iFOFC + 1)].Cell, 0, apCell[nCell], 0, szCell[nCell]);
}
else
{
Buffer.BlockCopy(pOld.Data, iFOFC, apCell[nCell], 0, szCell[nCell]);
}
nCell++;
}
}
else
{
var aData = pOld.Data;
var maskPage = pOld.MaskPage;
var cellOffset = pOld.CellOffset;
for (j = 0; j < limit; j++)
{
Debugger.Break();
Debug.Assert(nCell < nMaxCells);
apCell[nCell] = FindCellv2(aData, maskPage, cellOffset, j);
szCell[nCell] = pOld.cellSizePtr(apCell[nCell]);
nCell++;
}
}
if (i < nOld - 1 && 0 == leafData)
{
var sz = (ushort)szNew[i];
var pTemp = MallocEx.sqlite3Malloc(sz + leafCorrection);
Debug.Assert(nCell < nMaxCells);
szCell[nCell] = sz;
Debug.Assert(sz <= pBt.MaxLocal + 23);
Buffer.BlockCopy(pParent.Data, apDiv[i], pTemp, 0, sz);
if (apCell[nCell] == null || apCell[nCell].Length < sz)
{
Array.Resize(ref apCell[nCell], sz);
}
Buffer.BlockCopy(pTemp, leafCorrection, apCell[nCell], 0, sz);
Debug.Assert(leafCorrection == 0 || leafCorrection == 4);
szCell[nCell] = (ushort)(szCell[nCell] - leafCorrection);
if (0 == pOld.Leaf)
{
Debug.Assert(leafCorrection == 0);
Debug.Assert(pOld.HeaderOffset == 0);
// The right pointer of the child page pOld becomes the left pointer of the divider cell
Buffer.BlockCopy(pOld.Data, 8, apCell[nCell], 0, 4);//memcpy( apCell[nCell], ref pOld.aData[8], 4 );
}
else
{
Debug.Assert(leafCorrection == 4);
if (szCell[nCell] < 4)
{
// Do not allow any cells smaller than 4 bytes.
szCell[nCell] = 4;
}
}
nCell++;
}
}
// Figure out the number of pages needed to hold all nCell cells. Store this number in "k". Also compute szNew[] which is the total
// size of all cells on the i-th page and cntNew[] which is the index in apCell[] of the cell that divides page i from page i+1.
// cntNew[k] should equal nCell.
// Values computed by this block:
// k: The total number of sibling pages
// szNew[i]: Spaced used on the i-th sibling page.
// cntNew[i]: Index in apCell[] and szCell[] for the first cell to
// the right of the i-th sibling page.
// usableSpace: Number of bytes of space available on each sibling.
usableSpace = (int)pBt.UsableSize - 12 + leafCorrection;
int k;
for (subtotal = k = i = 0; i < nCell; i++)
{
Debug.Assert(i < nMaxCells);
subtotal += szCell[i] + 2;
if (subtotal > usableSpace)
{
szNew[k] = subtotal - szCell[i];
cntNew[k] = i;
if (leafData != 0)
{
i--;
}
subtotal = 0;
k++;
if (k > NB + 1)
{
rc = SysEx.SQLITE_CORRUPT_BKPT();
goto balance_cleanup;
}
}
}
szNew[k] = subtotal;
cntNew[k] = nCell;
k++;
// The packing computed by the previous block is biased toward the siblings on the left side. The left siblings are always nearly full, while the
// right-most sibling might be nearly empty. This block of code attempts to adjust the packing of siblings to get a better balance.
//
// This adjustment is more than an optimization. The packing above might be so out of balance as to be illegal. For example, the right-most
// sibling might be completely empty. This adjustment is not optional.
for (i = k - 1; i > 0; i--)
{
var szRight = szNew[i]; // Size of sibling on the right
var szLeft = szNew[i - 1]; // Size of sibling on the left
var r = cntNew[i - 1] - 1; // Index of right-most cell in left sibling
var d = r + 1 - leafData; // Index of first cell to the left of right sibling
Debug.Assert(d < nMaxCells);
Debug.Assert(r < nMaxCells);
while (szRight == 0 || szRight + szCell[d] + 2 <= szLeft - (szCell[r] + 2))
{
szRight += szCell[d] + 2;
szLeft -= szCell[r] + 2;
cntNew[i - 1]--;
r = cntNew[i - 1] - 1;
d = r + 1 - leafData;
}
szNew[i] = szRight;
szNew[i - 1] = szLeft;
}
// Either we found one or more cells (cntnew[0])>0) or pPage is a virtual root page. A virtual root page is when the real root
// page is page 1 and we are the only child of that page.
Debug.Assert(cntNew[0] > 0 || (pParent.ID == 1 && pParent.Cells == 0));
Btree.TRACE("BALANCE: old: %d %d %d ", apOld[0].ID, (nOld >= 2 ? apOld[1].ID : 0), (nOld >= 3 ? apOld[2].ID : 0));
// Allocate k new pages. Reuse old pages where possible.
if (apOld[0].ID <= 1)
{
rc = SysEx.SQLITE_CORRUPT_BKPT();
goto balance_cleanup;
}
pageFlags = apOld[0].Data[0];
for (i = 0; i < k; i++)
{
var pNew = new MemPage();
if (i < nOld)
{
pNew = apNew[i] = apOld[i];
apOld[i] = null;
rc = Pager.Write(pNew.DbPage);
nNew++;
if (rc != RC.OK)
{
goto balance_cleanup;
}
}
else
{
Debug.Assert(i > 0);
rc = pBt.allocateBtreePage(ref pNew, ref pgno, pgno, 0);
if (rc != 0)
{
goto balance_cleanup;
}
apNew[i] = pNew;
nNew++;
// Set the pointer-map entry for the new sibling page.
#if !SQLITE_OMIT_AUTOVACUUM
if (pBt.AutoVacuum)
#else
if (false)
#endif
{
pBt.ptrmapPut(pNew.ID, PTRMAP.BTREE, pParent.ID, ref rc);
if (rc != RC.OK)
{
goto balance_cleanup;
}
}
}
}
// Free any old pages that were not reused as new pages.
while (i < nOld)
{
apOld[i].freePage(ref rc);
if (rc != RC.OK)
{
goto balance_cleanup;
}
apOld[i].releasePage();
apOld[i] = null;
i++;
}
// Put the new pages in accending order. This helps to keep entries in the disk file in order so that a scan
// of the table is a linear scan through the file. That in turn helps the operating system to deliver pages
// from the disk more rapidly.
// An O(n^2) insertion sort algorithm is used, but since n is never more than NB (a small constant), that should
// not be a problem.
// When NB==3, this one optimization makes the database about 25% faster for large insertions and deletions.
for (i = 0; i < k - 1; i++)
{
var minV = (int)apNew[i].ID;
var minI = i;
for (j = i + 1; j < k; j++)
{
if (apNew[j].ID < (uint)minV)
{
minI = j;
minV = (int)apNew[j].ID;
}
}
if (minI > i)
{
var pT = apNew[i];
apNew[i] = apNew[minI];
apNew[minI] = pT;
}
}
Btree.TRACE("new: %d(%d) %d(%d) %d(%d) %d(%d) %d(%d)\n", apNew[0].ID, szNew[0],
(nNew >= 2 ? apNew[1].ID : 0), (nNew >= 2 ? szNew[1] : 0),
(nNew >= 3 ? apNew[2].ID : 0), (nNew >= 3 ? szNew[2] : 0),
(nNew >= 4 ? apNew[3].ID : 0), (nNew >= 4 ? szNew[3] : 0),
(nNew >= 5 ? apNew[4].ID : 0), (nNew >= 5 ? szNew[4] : 0));
Debug.Assert(Pager.IsPageWriteable(pParent.DbPage));
ConvertEx.Put4L(pParent.Data, pRight, apNew[nNew - 1].ID);
// Evenly distribute the data in apCell[] across the new pages. Insert divider cells into pParent as necessary.
j = 0;
for (i = 0; i < nNew; i++)
{
// Assemble the new sibling page.
MemPage pNew = apNew[i];
Debug.Assert(j < nMaxCells);
pNew.zeroPage(pageFlags);
pNew.assemblePage(cntNew[i] - j, apCell, szCell, j);
Debug.Assert(pNew.Cells > 0 || (nNew == 1 && cntNew[0] == 0));
Debug.Assert(pNew.NOverflows == 0);
j = cntNew[i];
// If the sibling page assembled above was not the right-most sibling, insert a divider cell into the parent page.
Debug.Assert(i < nNew - 1 || j == nCell);
if (j < nCell)
{
Debug.Assert(j < nMaxCells);
var pCell = apCell[j];
var sz = szCell[j] + leafCorrection;
var pTemp = MallocEx.sqlite3Malloc(sz);
if (pNew.Leaf == 0)
{
Buffer.BlockCopy(pCell, 0, pNew.Data, 8, 4);
}
else if (leafData != 0)
{
// If the tree is a leaf-data tree, and the siblings are leaves, then there is no divider cell in apCell[]. Instead, the divider
// cell consists of the integer key for the right-most cell of the sibling-page assembled above only.
var info = new CellInfo();
j--;
pNew.btreeParseCellPtr(apCell[j], ref info);
pCell = pTemp;
sz = 4 + ConvertEx.PutVarint9L(pCell, 4, (ulong)info.nKey);
pTemp = null;
}
else
{
//------------ pCell -= 4;
var _pCell_4 = MallocEx.sqlite3Malloc(pCell.Length + 4);
Buffer.BlockCopy(pCell, 0, _pCell_4, 4, pCell.Length);
pCell = _pCell_4;
// Obscure case for non-leaf-data trees: If the cell at pCell was previously stored on a leaf node, and its reported size was 4
// bytes, then it may actually be smaller than this (see btreeParseCellPtr(), 4 bytes is the minimum size of
// any cell). But it is important to pass the correct size to insertCell(), so reparse the cell now.
// Note that this can never happen in an SQLite data file, as all cells are at least 4 bytes. It only happens in b-trees used
// to evaluate "IN (SELECT ...)" and similar clauses.
if (szCell[j] == 4)
{
Debug.Assert(leafCorrection == 4);
sz = pParent.cellSizePtr(pCell);
}
}
iOvflSpace += sz;
Debug.Assert(sz <= pBt.MaxLocal + 23);
Debug.Assert(iOvflSpace <= (int)pBt.PageSize);
pParent.insertCell(nxDiv, pCell, sz, pTemp, pNew.ID, ref rc);
if (rc != RC.OK)
{
goto balance_cleanup;
}
Debug.Assert(Pager.IsPageWriteable(pParent.DbPage));
j++;
nxDiv++;
}
}
Debug.Assert(j == nCell);
Debug.Assert(nOld > 0);
Debug.Assert(nNew > 0);
if ((pageFlags & Btree.PTF_LEAF) == 0)
{
Buffer.BlockCopy(apCopy[nOld - 1].Data, 8, apNew[nNew - 1].Data, 8, 4);
}
if (isRoot != 0 && pParent.Cells == 0 && pParent.HeaderOffset <= apNew[0].FreeBytes)
{
// The root page of the b-tree now contains no cells. The only sibling page is the right-child of the parent. Copy the contents of the
// child page into the parent, decreasing the overall height of the b-tree structure by one. This is described as the "balance-shallower"
// sub-algorithm in some documentation.
// If this is an auto-vacuum database, the call to copyNodeContent() sets all pointer-map entries corresponding to database image pages
// for which the pointer is stored within the content being copied.
// The second Debug.Assert below verifies that the child page is defragmented (it must be, as it was just reconstructed using assemblePage()). This
// is important if the parent page happens to be page 1 of the database image. */
Debug.Assert(nNew == 1);
Debug.Assert(apNew[0].FreeBytes == (ConvertEx.Get2(apNew[0].Data, 5) - apNew[0].CellOffset - apNew[0].Cells * 2));
copyNodeContent(apNew[0], pParent, ref rc);
apNew[0].freePage(ref rc);
}
else
#if !SQLITE_OMIT_AUTOVACUUM
if (pBt.AutoVacuum)
#else
if (false)
#endif
{
// Fix the pointer-map entries for all the cells that were shifted around. There are several different types of pointer-map entries that need to
// be dealt with by this routine. Some of these have been set already, but many have not. The following is a summary:
// 1) The entries associated with new sibling pages that were not siblings when this function was called. These have already
// been set. We don't need to worry about old siblings that were moved to the free-list - the freePage() code has taken care
// of those.
// 2) The pointer-map entries associated with the first overflow page in any overflow chains used by new divider cells. These
// have also already been taken care of by the insertCell() code.
// 3) If the sibling pages are not leaves, then the child pages of cells stored on the sibling pages may need to be updated.
// 4) If the sibling pages are not internal intkey nodes, then any overflow pages used by these cells may need to be updated
// (internal intkey nodes never contain pointers to overflow pages).
// 5) If the sibling pages are not leaves, then the pointer-map entries for the right-child pages of each sibling may need
// to be updated.
// Cases 1 and 2 are dealt with above by other code. The next block deals with cases 3 and 4 and the one after that, case 5. Since
// setting a pointer map entry is a relatively expensive operation, this code only sets pointer map entries for child or overflow pages that have
// actually moved between pages.
var pNew = apNew[0];
var pOld = apCopy[0];
var nOverflow = pOld.NOverflows;
var iNextOld = pOld.Cells + nOverflow;
var iOverflow = (nOverflow != 0 ? pOld.Overflows[0].Index : -1);
j = 0; // Current 'old' sibling page
k = 0; // Current 'new' sibling page
for (i = 0; i < nCell; i++)
{
var isDivider = 0;
while (i == iNextOld)
{
// Cell i is the cell immediately following the last cell on old sibling page j. If the siblings are not leaf pages of an
// intkey b-tree, then cell i was a divider cell.
pOld = apCopy[++j];
iNextOld = i + (0 == leafData ? 1 : 0) + pOld.Cells + pOld.NOverflows;
if (pOld.NOverflows != 0)
{
nOverflow = pOld.NOverflows;
iOverflow = i + (0 == leafData ? 1 : 0) + pOld.Overflows[0].Index;
}
isDivider = 0 == leafData ? 1 : 0;
}
Debug.Assert(nOverflow > 0 || iOverflow < i);
Debug.Assert(nOverflow < 2 || pOld.Overflows[0].Index == pOld.Overflows[1].Index - 1);
Debug.Assert(nOverflow < 3 || pOld.Overflows[1].Index == pOld.Overflows[2].Index - 1);
if (i == iOverflow)
{
isDivider = 1;
if (--nOverflow > 0)
{
iOverflow++;
}
}
if (i == cntNew[k])
{
// Cell i is the cell immediately following the last cell on new sibling page k. If the siblings are not leaf pages of an
// intkey b-tree, then cell i is a divider cell.
pNew = apNew[++k];
if (leafData == 0)
{
continue;
}
}
Debug.Assert(j < nOld);
Debug.Assert(k < nNew);
// If the cell was originally divider cell (and is not now) or an overflow cell, or if the cell was located on a different sibling
// page before the balancing, then the pointer map entries associated with any child or overflow pages need to be updated.
if (isDivider != 0 || pOld.ID != pNew.ID)
{
if (leafCorrection == 0)
{
pBt.ptrmapPut(ConvertEx.Get4(apCell[i]), PTRMAP.BTREE, pNew.ID, ref rc);
}
if (szCell[i] > pNew.MinLocal)
{
pNew.ptrmapPutOvflPtr(apCell[i], ref rc);
}
}
}
if (leafCorrection == 0)
{
for (i = 0; i < nNew; i++)
{
var key = ConvertEx.Get4(apNew[i].Data, 8);
pBt.ptrmapPut(key, PTRMAP.BTREE, apNew[i].ID, ref rc);
}
}
#if false
// The ptrmapCheckPages() contains Debug.Assert() statements that verify that all pointer map pages are set correctly. This is helpful while
// debugging. This is usually disabled because a corrupt database may cause an Debug.Assert() statement to fail.
ptrmapCheckPages(apNew, nNew);
ptrmapCheckPages(pParent, 1);
#endif
}
Debug.Assert(pParent.HasInit);
Btree.TRACE("BALANCE: finished: old=%d new=%d cells=%d\n", nOld, nNew, nCell);
// Cleanup before returning.
balance_cleanup:
MallocEx.sqlite3ScratchFree(apCell);
for (i = 0; i < nOld; i++)
{
apOld[i].releasePage();
}
for (i = 0; i < nNew; i++)
{
apNew[i].releasePage();
}
return(rc);
}
internal static RC balance_nonroot(MemPage pParent, int iParentIdx, byte[] aOvflSpace, int isRoot)
{
var apOld = new MemPage[NB]; // pPage and up to two siblings
var apCopy = new MemPage[NB]; // Private copies of apOld[] pages
var apNew = new MemPage[NB + 2];// pPage and up to NB siblings after balancing
var apDiv = new int[NB - 1]; // Divider cells in pParent
var cntNew = new int[NB + 2]; // Index in aCell[] of cell after i-th page
var szNew = new int[NB + 2]; // Combined size of cells place on i-th page
var szCell = new ushort[1]; // Local size of all cells in apCell[]
BtShared pBt; // The whole database
int nCell = 0; // Number of cells in apCell[]
int nMaxCells = 0; // Allocated size of apCell, szCell, aFrom.
int nNew = 0; // Number of pages in apNew[]
ushort leafCorrection; // 4 if pPage is a leaf. 0 if not
int leafData; // True if pPage is a leaf of a LEAFDATA tree
int usableSpace; // Bytes in pPage beyond the header
int pageFlags; // Value of pPage.aData[0]
int subtotal; // Subtotal of bytes in cells on one page
int iOvflSpace = 0; // First unused byte of aOvflSpace[]
//int szScratch; // Size of scratch memory requested
byte[][] apCell = null; // All cells begin balanced
//
pBt = pParent.Shared;
Debug.Assert(MutexEx.Held(pBt.Mutex));
Debug.Assert(Pager.IsPageWriteable(pParent.DbPage));
#if false
Btree.TRACE("BALANCE: begin page %d child of %d\n", pPage.pgno, pParent.pgno);
#endif
// At this point pParent may have at most one overflow cell. And if this overflow cell is present, it must be the cell with
// index iParentIdx. This scenario comes about when this function is called (indirectly) from sqlite3BtreeDelete().
Debug.Assert(pParent.NOverflows == 0 || pParent.NOverflows == 1);
Debug.Assert(pParent.NOverflows == 0 || pParent.Overflows[0].Index == iParentIdx);
// Find the sibling pages to balance. Also locate the cells in pParent that divide the siblings. An attempt is made to find NN siblings on
// either side of pPage. More siblings are taken from one side, however, if there are fewer than NN siblings on the other side. If pParent
// has NB or fewer children then all children of pParent are taken.
// This loop also drops the divider cells from the parent page. This way, the remainder of the function does not have to deal with any
// overflow cells in the parent page, since if any existed they will have already been removed.
int nOld; // Number of pages in apOld[]
int nxDiv; // Next divider slot in pParent.aCell[]
var i = pParent.NOverflows + pParent.Cells;
if (i < 2)
{
nxDiv = 0;
nOld = i + 1;
}
else
{
nOld = 3;
if (iParentIdx == 0)
nxDiv = 0;
else if (iParentIdx == i)
nxDiv = i - 2;
else
nxDiv = iParentIdx - 1;
i = 2;
}
var pRight = ((i + nxDiv - pParent.NOverflows) == pParent.Cells ? pParent.HeaderOffset + 8 : pParent.FindCell(i + nxDiv - pParent.NOverflows)); // Location in parent of right-sibling pointer
var pgno = (Pgno)ConvertEx.Get4(pParent.Data, pRight);
var rc = RC.OK;
while (true)
{
rc = pBt.getAndInitPage(pgno, ref apOld[i]);
if (rc != RC.OK)
goto balance_cleanup;
nMaxCells += 1 + apOld[i].Cells + apOld[i].NOverflows;
if (i-- == 0)
break;
if (i + nxDiv == pParent.Overflows[0].Index && pParent.NOverflows != 0)
{
apDiv[i] = 0;
pgno = ConvertEx.Get4(pParent.Overflows[0].Cell, apDiv[i]);
szNew[i] = pParent.cellSizePtr(apDiv[i]);
pParent.NOverflows = 0;
}
else
{
apDiv[i] = pParent.FindCell(i + nxDiv - pParent.NOverflows);
pgno = ConvertEx.Get4(pParent.Data, apDiv[i]);
szNew[i] = pParent.cellSizePtr(apDiv[i]);
// Drop the cell from the parent page. apDiv[i] still points to the cell within the parent, even though it has been dropped.
// This is safe because dropping a cell only overwrites the first four bytes of it, and this function does not need the first
// four bytes of the divider cell. So the pointer is safe to use later on.
//
// Unless SQLite is compiled in secure-delete mode. In this case, the dropCell() routine will overwrite the entire cell with zeroes.
// In this case, temporarily copy the cell into the aOvflSpace[] buffer. It will be copied out again as soon as the aSpace[] buffer
// is allocated.
//if (pBt.secureDelete)
//{
// int iOff = (int)(apDiv[i]) - (int)(pParent.aData); //SQLITE_PTR_TO_INT(apDiv[i]) - SQLITE_PTR_TO_INT(pParent.aData);
// if( (iOff+szNew[i])>(int)pBt->usableSize )
// {
// rc = SQLITE_CORRUPT_BKPT();
// Array.Clear(apOld[0].aData,0,apOld[0].aData.Length); //memset(apOld, 0, (i + 1) * sizeof(MemPage*));
// goto balance_cleanup;
// }
// else
// {
// memcpy(&aOvflSpace[iOff], apDiv[i], szNew[i]);
// apDiv[i] = &aOvflSpace[apDiv[i] - pParent.aData];
// }
//}
pParent.dropCell(i + nxDiv - pParent.NOverflows, szNew[i], ref rc);
}
}
// Make nMaxCells a multiple of 4 in order to preserve 8-byte alignment
nMaxCells = (nMaxCells + 3) & ~3;
// Allocate space for memory structures
apCell = MallocEx.sqlite3ScratchMalloc(apCell, nMaxCells);
if (szCell.Length < nMaxCells)
Array.Resize(ref szCell, nMaxCells);
// Load pointers to all cells on sibling pages and the divider cells into the local apCell[] array. Make copies of the divider cells
// into space obtained from aSpace1[] and remove the the divider Cells from pParent.
// If the siblings are on leaf pages, then the child pointers of the divider cells are stripped from the cells before they are copied
// into aSpace1[]. In this way, all cells in apCell[] are without child pointers. If siblings are not leaves, then all cell in
// apCell[] include child pointers. Either way, all cells in apCell[] are alike.
// leafCorrection: 4 if pPage is a leaf. 0 if pPage is not a leaf.
// leafData: 1 if pPage holds key+data and pParent holds only keys.
leafCorrection = (ushort)(apOld[0].Leaf * 4);
leafData = apOld[0].HasData;
int j;
for (i = 0; i < nOld; i++)
{
// Before doing anything else, take a copy of the i'th original sibling The rest of this function will use data from the copies rather
// that the original pages since the original pages will be in the process of being overwritten.
var pOld = apCopy[i] = apOld[i].Clone();
var limit = pOld.Cells + pOld.NOverflows;
if (pOld.NOverflows > 0 || true)
{
for (j = 0; j < limit; j++)
{
Debug.Assert(nCell < nMaxCells);
var iFOFC = pOld.FindOverflowCell(j);
szCell[nCell] = pOld.cellSizePtr(iFOFC);
// Copy the Data Locally
if (apCell[nCell] == null)
apCell[nCell] = new byte[szCell[nCell]];
else if (apCell[nCell].Length < szCell[nCell])
Array.Resize(ref apCell[nCell], szCell[nCell]);
if (iFOFC < 0) // Overflow Cell
Buffer.BlockCopy(pOld.Overflows[-(iFOFC + 1)].Cell, 0, apCell[nCell], 0, szCell[nCell]);
else
Buffer.BlockCopy(pOld.Data, iFOFC, apCell[nCell], 0, szCell[nCell]);
nCell++;
}
}
else
{
var aData = pOld.Data;
var maskPage = pOld.MaskPage;
var cellOffset = pOld.CellOffset;
for (j = 0; j < limit; j++)
{
Debugger.Break();
Debug.Assert(nCell < nMaxCells);
apCell[nCell] = FindCellv2(aData, maskPage, cellOffset, j);
szCell[nCell] = pOld.cellSizePtr(apCell[nCell]);
nCell++;
}
}
if (i < nOld - 1 && 0 == leafData)
{
var sz = (ushort)szNew[i];
var pTemp = MallocEx.sqlite3Malloc(sz + leafCorrection);
Debug.Assert(nCell < nMaxCells);
szCell[nCell] = sz;
Debug.Assert(sz <= pBt.MaxLocal + 23);
Buffer.BlockCopy(pParent.Data, apDiv[i], pTemp, 0, sz);
if (apCell[nCell] == null || apCell[nCell].Length < sz)
Array.Resize(ref apCell[nCell], sz);
Buffer.BlockCopy(pTemp, leafCorrection, apCell[nCell], 0, sz);
Debug.Assert(leafCorrection == 0 || leafCorrection == 4);
szCell[nCell] = (ushort)(szCell[nCell] - leafCorrection);
if (0 == pOld.Leaf)
{
Debug.Assert(leafCorrection == 0);
Debug.Assert(pOld.HeaderOffset == 0);
// The right pointer of the child page pOld becomes the left pointer of the divider cell
Buffer.BlockCopy(pOld.Data, 8, apCell[nCell], 0, 4);//memcpy( apCell[nCell], ref pOld.aData[8], 4 );
}
else
{
Debug.Assert(leafCorrection == 4);
if (szCell[nCell] < 4)
// Do not allow any cells smaller than 4 bytes.
szCell[nCell] = 4;
}
nCell++;
}
}
// Figure out the number of pages needed to hold all nCell cells. Store this number in "k". Also compute szNew[] which is the total
// size of all cells on the i-th page and cntNew[] which is the index in apCell[] of the cell that divides page i from page i+1.
// cntNew[k] should equal nCell.
// Values computed by this block:
// k: The total number of sibling pages
// szNew[i]: Spaced used on the i-th sibling page.
// cntNew[i]: Index in apCell[] and szCell[] for the first cell to
// the right of the i-th sibling page.
// usableSpace: Number of bytes of space available on each sibling.
usableSpace = (int)pBt.UsableSize - 12 + leafCorrection;
int k;
for (subtotal = k = i = 0; i < nCell; i++)
{
Debug.Assert(i < nMaxCells);
subtotal += szCell[i] + 2;
if (subtotal > usableSpace)
{
szNew[k] = subtotal - szCell[i];
cntNew[k] = i;
if (leafData != 0)
i--;
subtotal = 0;
k++;
if (k > NB + 1)
{
rc = SysEx.SQLITE_CORRUPT_BKPT();
goto balance_cleanup;
}
}
}
szNew[k] = subtotal;
cntNew[k] = nCell;
k++;
// The packing computed by the previous block is biased toward the siblings on the left side. The left siblings are always nearly full, while the
// right-most sibling might be nearly empty. This block of code attempts to adjust the packing of siblings to get a better balance.
//
// This adjustment is more than an optimization. The packing above might be so out of balance as to be illegal. For example, the right-most
// sibling might be completely empty. This adjustment is not optional.
for (i = k - 1; i > 0; i--)
{
var szRight = szNew[i]; // Size of sibling on the right
var szLeft = szNew[i - 1]; // Size of sibling on the left
var r = cntNew[i - 1] - 1; // Index of right-most cell in left sibling
var d = r + 1 - leafData; // Index of first cell to the left of right sibling
Debug.Assert(d < nMaxCells);
Debug.Assert(r < nMaxCells);
while (szRight == 0 || szRight + szCell[d] + 2 <= szLeft - (szCell[r] + 2))
{
szRight += szCell[d] + 2;
szLeft -= szCell[r] + 2;
cntNew[i - 1]--;
r = cntNew[i - 1] - 1;
d = r + 1 - leafData;
}
szNew[i] = szRight;
szNew[i - 1] = szLeft;
}
// Either we found one or more cells (cntnew[0])>0) or pPage is a virtual root page. A virtual root page is when the real root
// page is page 1 and we are the only child of that page.
Debug.Assert(cntNew[0] > 0 || (pParent.ID == 1 && pParent.Cells == 0));
Btree.TRACE("BALANCE: old: %d %d %d ", apOld[0].ID, (nOld >= 2 ? apOld[1].ID : 0), (nOld >= 3 ? apOld[2].ID : 0));
// Allocate k new pages. Reuse old pages where possible.
if (apOld[0].ID <= 1)
{
rc = SysEx.SQLITE_CORRUPT_BKPT();
goto balance_cleanup;
}
pageFlags = apOld[0].Data[0];
for (i = 0; i < k; i++)
{
var pNew = new MemPage();
if (i < nOld)
{
pNew = apNew[i] = apOld[i];
apOld[i] = null;
rc = Pager.Write(pNew.DbPage);
nNew++;
if (rc != RC.OK)
goto balance_cleanup;
}
else
{
Debug.Assert(i > 0);
rc = pBt.allocateBtreePage(ref pNew, ref pgno, pgno, 0);
if (rc != 0)
goto balance_cleanup;
apNew[i] = pNew;
nNew++;
// Set the pointer-map entry for the new sibling page.
#if !SQLITE_OMIT_AUTOVACUUM
if (pBt.AutoVacuum)
#else
if (false)
#endif
{
pBt.ptrmapPut(pNew.ID, PTRMAP.BTREE, pParent.ID, ref rc);
if (rc != RC.OK)
goto balance_cleanup;
}
}
}
// Free any old pages that were not reused as new pages.
while (i < nOld)
{
apOld[i].freePage(ref rc);
if (rc != RC.OK)
goto balance_cleanup;
apOld[i].releasePage();
apOld[i] = null;
i++;
}
// Put the new pages in accending order. This helps to keep entries in the disk file in order so that a scan
// of the table is a linear scan through the file. That in turn helps the operating system to deliver pages
// from the disk more rapidly.
// An O(n^2) insertion sort algorithm is used, but since n is never more than NB (a small constant), that should
// not be a problem.
// When NB==3, this one optimization makes the database about 25% faster for large insertions and deletions.
for (i = 0; i < k - 1; i++)
{
var minV = (int)apNew[i].ID;
var minI = i;
for (j = i + 1; j < k; j++)
if (apNew[j].ID < (uint)minV)
{
minI = j;
minV = (int)apNew[j].ID;
}
if (minI > i)
{
var pT = apNew[i];
apNew[i] = apNew[minI];
apNew[minI] = pT;
}
}
Btree.TRACE("new: %d(%d) %d(%d) %d(%d) %d(%d) %d(%d)\n", apNew[0].ID, szNew[0],
(nNew >= 2 ? apNew[1].ID : 0), (nNew >= 2 ? szNew[1] : 0),
(nNew >= 3 ? apNew[2].ID : 0), (nNew >= 3 ? szNew[2] : 0),
(nNew >= 4 ? apNew[3].ID : 0), (nNew >= 4 ? szNew[3] : 0),
(nNew >= 5 ? apNew[4].ID : 0), (nNew >= 5 ? szNew[4] : 0));
Debug.Assert(Pager.IsPageWriteable(pParent.DbPage));
ConvertEx.Put4L(pParent.Data, pRight, apNew[nNew - 1].ID);
// Evenly distribute the data in apCell[] across the new pages. Insert divider cells into pParent as necessary.
j = 0;
for (i = 0; i < nNew; i++)
{
// Assemble the new sibling page.
MemPage pNew = apNew[i];
Debug.Assert(j < nMaxCells);
pNew.zeroPage(pageFlags);
pNew.assemblePage(cntNew[i] - j, apCell, szCell, j);
Debug.Assert(pNew.Cells > 0 || (nNew == 1 && cntNew[0] == 0));
Debug.Assert(pNew.NOverflows == 0);
j = cntNew[i];
// If the sibling page assembled above was not the right-most sibling, insert a divider cell into the parent page.
Debug.Assert(i < nNew - 1 || j == nCell);
if (j < nCell)
{
Debug.Assert(j < nMaxCells);
var pCell = apCell[j];
var sz = szCell[j] + leafCorrection;
var pTemp = MallocEx.sqlite3Malloc(sz);
if (pNew.Leaf == 0)
Buffer.BlockCopy(pCell, 0, pNew.Data, 8, 4);
else if (leafData != 0)
{
// If the tree is a leaf-data tree, and the siblings are leaves, then there is no divider cell in apCell[]. Instead, the divider
// cell consists of the integer key for the right-most cell of the sibling-page assembled above only.
var info = new CellInfo();
j--;
pNew.btreeParseCellPtr(apCell[j], ref info);
pCell = pTemp;
sz = 4 + ConvertEx.PutVarint9L(pCell, 4, (ulong)info.nKey);
pTemp = null;
}
else
{
//------------ pCell -= 4;
var _pCell_4 = MallocEx.sqlite3Malloc(pCell.Length + 4);
Buffer.BlockCopy(pCell, 0, _pCell_4, 4, pCell.Length);
pCell = _pCell_4;
// Obscure case for non-leaf-data trees: If the cell at pCell was previously stored on a leaf node, and its reported size was 4
// bytes, then it may actually be smaller than this (see btreeParseCellPtr(), 4 bytes is the minimum size of
// any cell). But it is important to pass the correct size to insertCell(), so reparse the cell now.
// Note that this can never happen in an SQLite data file, as all cells are at least 4 bytes. It only happens in b-trees used
// to evaluate "IN (SELECT ...)" and similar clauses.
if (szCell[j] == 4)
{
Debug.Assert(leafCorrection == 4);
sz = pParent.cellSizePtr(pCell);
}
}
iOvflSpace += sz;
Debug.Assert(sz <= pBt.MaxLocal + 23);
Debug.Assert(iOvflSpace <= (int)pBt.PageSize);
pParent.insertCell(nxDiv, pCell, sz, pTemp, pNew.ID, ref rc);
if (rc != RC.OK)
goto balance_cleanup;
Debug.Assert(Pager.IsPageWriteable(pParent.DbPage));
j++;
nxDiv++;
}
}
Debug.Assert(j == nCell);
Debug.Assert(nOld > 0);
Debug.Assert(nNew > 0);
if ((pageFlags & Btree.PTF_LEAF) == 0)
Buffer.BlockCopy(apCopy[nOld - 1].Data, 8, apNew[nNew - 1].Data, 8, 4);
if (isRoot != 0 && pParent.Cells == 0 && pParent.HeaderOffset <= apNew[0].FreeBytes)
{
// The root page of the b-tree now contains no cells. The only sibling page is the right-child of the parent. Copy the contents of the
// child page into the parent, decreasing the overall height of the b-tree structure by one. This is described as the "balance-shallower"
// sub-algorithm in some documentation.
// If this is an auto-vacuum database, the call to copyNodeContent() sets all pointer-map entries corresponding to database image pages
// for which the pointer is stored within the content being copied.
// The second Debug.Assert below verifies that the child page is defragmented (it must be, as it was just reconstructed using assemblePage()). This
// is important if the parent page happens to be page 1 of the database image. */
Debug.Assert(nNew == 1);
Debug.Assert(apNew[0].FreeBytes == (ConvertEx.Get2(apNew[0].Data, 5) - apNew[0].CellOffset - apNew[0].Cells * 2));
copyNodeContent(apNew[0], pParent, ref rc);
apNew[0].freePage(ref rc);
}
else
#if !SQLITE_OMIT_AUTOVACUUM
if (pBt.AutoVacuum)
#else
if (false)
#endif
{
// Fix the pointer-map entries for all the cells that were shifted around. There are several different types of pointer-map entries that need to
// be dealt with by this routine. Some of these have been set already, but many have not. The following is a summary:
// 1) The entries associated with new sibling pages that were not siblings when this function was called. These have already
// been set. We don't need to worry about old siblings that were moved to the free-list - the freePage() code has taken care
// of those.
// 2) The pointer-map entries associated with the first overflow page in any overflow chains used by new divider cells. These
// have also already been taken care of by the insertCell() code.
// 3) If the sibling pages are not leaves, then the child pages of cells stored on the sibling pages may need to be updated.
// 4) If the sibling pages are not internal intkey nodes, then any overflow pages used by these cells may need to be updated
// (internal intkey nodes never contain pointers to overflow pages).
// 5) If the sibling pages are not leaves, then the pointer-map entries for the right-child pages of each sibling may need
// to be updated.
// Cases 1 and 2 are dealt with above by other code. The next block deals with cases 3 and 4 and the one after that, case 5. Since
// setting a pointer map entry is a relatively expensive operation, this code only sets pointer map entries for child or overflow pages that have
// actually moved between pages.
var pNew = apNew[0];
var pOld = apCopy[0];
var nOverflow = pOld.NOverflows;
var iNextOld = pOld.Cells + nOverflow;
var iOverflow = (nOverflow != 0 ? pOld.Overflows[0].Index : -1);
j = 0; // Current 'old' sibling page
k = 0; // Current 'new' sibling page
for (i = 0; i < nCell; i++)
{
var isDivider = 0;
while (i == iNextOld)
{
// Cell i is the cell immediately following the last cell on old sibling page j. If the siblings are not leaf pages of an
// intkey b-tree, then cell i was a divider cell.
pOld = apCopy[++j];
iNextOld = i + (0 == leafData ? 1 : 0) + pOld.Cells + pOld.NOverflows;
if (pOld.NOverflows != 0)
{
nOverflow = pOld.NOverflows;
iOverflow = i + (0 == leafData ? 1 : 0) + pOld.Overflows[0].Index;
}
isDivider = 0 == leafData ? 1 : 0;
}
Debug.Assert(nOverflow > 0 || iOverflow < i);
Debug.Assert(nOverflow < 2 || pOld.Overflows[0].Index == pOld.Overflows[1].Index - 1);
Debug.Assert(nOverflow < 3 || pOld.Overflows[1].Index == pOld.Overflows[2].Index - 1);
if (i == iOverflow)
{
isDivider = 1;
if (--nOverflow > 0)
iOverflow++;
}
if (i == cntNew[k])
{
// Cell i is the cell immediately following the last cell on new sibling page k. If the siblings are not leaf pages of an
// intkey b-tree, then cell i is a divider cell.
pNew = apNew[++k];
if (leafData == 0)
continue;
}
Debug.Assert(j < nOld);
Debug.Assert(k < nNew);
// If the cell was originally divider cell (and is not now) or an overflow cell, or if the cell was located on a different sibling
// page before the balancing, then the pointer map entries associated with any child or overflow pages need to be updated.
if (isDivider != 0 || pOld.ID != pNew.ID)
{
if (leafCorrection == 0)
pBt.ptrmapPut(ConvertEx.Get4(apCell[i]), PTRMAP.BTREE, pNew.ID, ref rc);
if (szCell[i] > pNew.MinLocal)
pNew.ptrmapPutOvflPtr(apCell[i], ref rc);
}
}
if (leafCorrection == 0)
for (i = 0; i < nNew; i++)
{
var key = ConvertEx.Get4(apNew[i].Data, 8);
pBt.ptrmapPut(key, PTRMAP.BTREE, apNew[i].ID, ref rc);
}
#if false
// The ptrmapCheckPages() contains Debug.Assert() statements that verify that all pointer map pages are set correctly. This is helpful while
// debugging. This is usually disabled because a corrupt database may cause an Debug.Assert() statement to fail.
ptrmapCheckPages(apNew, nNew);
ptrmapCheckPages(pParent, 1);
#endif
}
Debug.Assert(pParent.HasInit);
Btree.TRACE("BALANCE: finished: old=%d new=%d cells=%d\n", nOld, nNew, nCell);
// Cleanup before returning.
balance_cleanup:
MallocEx.sqlite3ScratchFree(apCell);
for (i = 0; i < nOld; i++)
apOld[i].releasePage();
for (i = 0; i < nNew; i++)
apNew[i].releasePage();
return rc;
}