Multiple overflow cells are always adjacent and sequential. Exploit this
invariant for a small size reduction and performance increase and add assert()s to prove the invariant. FossilOrigin-Name: f77f2f48f48e374a72b6c054142f7a3ec0b1483c
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12
manifest
@ -1,5 +1,5 @@
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C Faster\sloading\sof\scell\spointers\sinto\sthe\sb.apCell\sarray\sin\sbalance_nonroot.
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D 2015-06-23T17:09:53.066
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C Multiple\soverflow\scells\sare\salways\sadjacent\sand\ssequential.\s\sExploit\sthis\ninvariant\sfor\sa\ssmall\ssize\sreduction\sand\sperformance\sincrease\sand\sadd\nassert()s\sto\sprove\sthe\sinvariant.
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D 2015-06-23T18:24:25.456
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F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
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F Makefile.in 1063c58075b7400d93326b0eb332b48a54f53025
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F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
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@ -192,7 +192,7 @@ F src/auth.c b56c78ebe40a2110fd361379f7e8162d23f92240
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F src/backup.c ff743689c4d6c5cb55ad42ed9d174b2b3e71f1e3
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F src/bitvec.c 5eb7958c3bf65210211cbcfc44eff86d0ded7c9d
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F src/btmutex.c 45a968cc85afed9b5e6cf55bf1f42f8d18107f79
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F src/btree.c 0b20e8281ea9b2add9eef6f6c3f18433f2f47b53
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F src/btree.c ca394997680c8068a3ef87fd8ad55b1a7dad08a4
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F src/btree.h 969adc948e89e449220ff0ff724c94bb2a52e9f1
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F src/btreeInt.h 6ece2dd9c8e2eac05f0a8ded8772a44e96486c65
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F src/build.c b3f15255d5b16e42dafeaa638fd4f8a47c94ed70
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@ -1286,7 +1286,7 @@ F tool/vdbe_profile.tcl 67746953071a9f8f2f668b73fe899074e2c6d8c1
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F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
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F tool/warnings.sh 48bd54594752d5be3337f12c72f28d2080cb630b
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F tool/win/sqlite.vsix deb315d026cc8400325c5863eef847784a219a2f
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P 6319ee1256b1f7c39dd39a536a39b77b3d10dcac
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R ed68212da4042fbfd3887c9cc6d179ba
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P fda89b0512477f9da09fd0f4e548ed4b13efd49d
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R 8408184ce1eeef4fb81f9e80cd68a3ff
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U drh
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Z 1ac31720ec363831ce0715d2977b6c52
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Z f70e49c696aab72ebd6898ae9c8ebc72
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@ -1 +1 @@
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fda89b0512477f9da09fd0f4e548ed4b13efd49d
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f77f2f48f48e374a72b6c054142f7a3ec0b1483c
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64
src/btree.c
64
src/btree.c
@ -957,25 +957,6 @@ static int ptrmapGet(BtShared *pBt, Pgno key, u8 *pEType, Pgno *pPgno){
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#define findCell(P,I) \
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((P)->aData + ((P)->maskPage & get2byte(&(P)->aCellIdx[2*(I)])))
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/*
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** Sort the overflow cells of a page into index order.
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**
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** An O(N*N) algorithm is used. But that should not be a problem
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** since N is only very rarely more than 1.
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*/
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static void btreeSortOverflow(MemPage *p){
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int j, k;
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for(j=0; j<p->nOverflow-1; j++){
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for(k=j+1; k<p->nOverflow; k++){
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if( p->aiOvfl[j]>p->aiOvfl[k] ){
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SWAP(u16, p->aiOvfl[j], p->aiOvfl[k]);
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SWAP(u8*, p->apOvfl[j], p->apOvfl[k]);
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}
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}
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}
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}
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/*
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** This is common tail processing for btreeParseCellPtr() and
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** btreeParseCellPtrIndex() for the case when the cell does not fit entirely
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@ -6243,6 +6224,14 @@ static void insertCell(
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assert( j<(int)(sizeof(pPage->apOvfl)/sizeof(pPage->apOvfl[0])) );
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pPage->apOvfl[j] = pCell;
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pPage->aiOvfl[j] = (u16)i;
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/* When multiple overflows occur, they are always sequential and in
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** sorted order. This invariants arise because multiple overflows can
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** only occur when inserting divider cells into the parent page during
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** balancing, and the dividers are adjacent and sorted.
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*/
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assert( j==0 || pPage->aiOvfl[j-1]<(u16)i ); /* Overflows in sorted order */
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assert( j==0 || i==pPage->aiOvfl[j-1]+1 ); /* Overflows are sequential */
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}else{
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int rc = sqlite3PagerWrite(pPage->pDbPage);
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if( rc!=SQLITE_OK ){
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@ -7054,6 +7043,7 @@ static int balance_nonroot(
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u8 *aData = pOld->aData;
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u16 maskPage = pOld->maskPage;
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u8 *piCell = aData + pOld->cellOffset;
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u8 *piEnd;
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/* Verify that all sibling pages are of the same "type" (table-leaf,
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** table-interior, index-leaf, or index-interior).
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@ -7063,8 +7053,17 @@ static int balance_nonroot(
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goto balance_cleanup;
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}
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/* Load b.apCell[] with pointers to all cells in pOld. Intersperse
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** overflow cells in the correct sequence.
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/* Load b.apCell[] with pointers to all cells in pOld. If pOld
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** constains overflow cells, include them in the b.apCell[] array
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** in the correct spot.
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**
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** Note that when there are multiple overflow cells, it is always the
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** case that they are sequential and adjacent. This invariant arises
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** because multiple overflows can only occurs when inserting divider
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** cells into a parent on a prior balance, and divider cells are always
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** adjacent and are inserted in order. There is an assert() tagged
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** with "NOTE 1" in the overflow cell insertion loop to prove this
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** invariant.
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**
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** This must be done in advance. Once the balance starts, the cell
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** offset section of the btree page will be overwritten and we will no
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@ -7074,22 +7073,21 @@ static int balance_nonroot(
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memset(&b.szCell[b.nCell], 0, sizeof(b.szCell[0])*limit);
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if( pOld->nOverflow>0 ){
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memset(&b.szCell[b.nCell+limit], 0, sizeof(b.szCell[0])*pOld->nOverflow);
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btreeSortOverflow(pOld);
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for(j=k=0; k<pOld->nOverflow; k++){
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limit = pOld->aiOvfl[k] - k;
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while( j<limit ){
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b.apCell[b.nCell] = aData + (maskPage & get2byte(piCell));
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piCell += 2;
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b.nCell++;
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j++;
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}
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limit = pOld->aiOvfl[0];
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for(j=0; j<limit; j++){
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b.apCell[b.nCell] = aData + (maskPage & get2byte(piCell));
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piCell += 2;
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b.nCell++;
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}
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for(k=0; k<pOld->nOverflow; k++){
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assert( k==0 || pOld->aiOvfl[k-1]+1==pOld->aiOvfl[k] );/* NOTE 1 */
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b.apCell[b.nCell] = pOld->apOvfl[k];
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b.nCell++;
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}
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limit = pOld->nCell - j;
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limit = pOld->nCell - pOld->aiOvfl[0];
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}
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limit += b.nCell;
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while( b.nCell<limit ){
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piEnd = aData + pOld->cellOffset + 2*pOld->nCell;
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while( piCell<piEnd ){
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assert( b.nCell<nMaxCells );
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b.apCell[b.nCell] = aData + (maskPage & get2byte(piCell));
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piCell += 2;
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