/* * _bt_search() -- Search the tree for a particular scankey, * or more precisely for the first leaf page it could be on. * * The passed scankey must be an insertion-type scankey (see nbtree/README), * but it can omit the rightmost column(s) of the index. * * When nextkey is false (the usual case), we are looking for the first * item >= scankey. When nextkey is true, we are looking for the first * item strictly greater than scankey. * * Return value is a stack of parent-page pointers. *bufP is set to the * address of the leaf-page buffer, which is read-locked and pinned. * No locks are held on the parent pages, however! * * NOTE that the returned buffer is read-locked regardless of the access * parameter. However, access = BT_WRITE will allow an empty root page * to be created and returned. When access = BT_READ, an empty index * will result in *bufP being set to InvalidBuffer. Also, in BT_WRITE mode, * any incomplete splits encountered during the search will be finished. */ BTStack _bt_search(Relation rel, int keysz, ScanKey scankey, bool nextkey, Buffer *bufP, int access) { BTStack stack_in = NULL; /* Get the root page to start with */ *bufP = _bt_getroot(rel, access); /* If index is empty and access = BT_READ, no root page is created. */ if (!BufferIsValid(*bufP)) return (BTStack) NULL; /* Loop iterates once per level descended in the tree */ for (;;) { Page page; BTPageOpaque opaque; OffsetNumber offnum; ItemId itemid; IndexTuple itup; BlockNumber blkno; BlockNumber par_blkno; BTStack new_stack; /* * Race -- the page we just grabbed may have split since we read its * pointer in the parent (or metapage). If it has, we may need to * move right to its new sibling. Do that. * * In write-mode, allow _bt_moveright to finish any incomplete splits * along the way. Strictly speaking, we'd only need to finish an * incomplete split on the leaf page we're about to insert to, not on * any of the upper levels (they is taken care of in _bt_getstackbuf, * if the leaf page is split and we insert to the parent page). But * this is a good opportunity to finish splits of internal pages too. */ *bufP = _bt_moveright(rel, *bufP, keysz, scankey, nextkey, (access == BT_WRITE), stack_in, BT_READ); /* if this is a leaf page, we're done */ page = BufferGetPage(*bufP); opaque = (BTPageOpaque) PageGetSpecialPointer(page); if (P_ISLEAF(opaque)) break; /* * Find the appropriate item on the internal page, and get the child * page that it points to. */ offnum = _bt_binsrch(rel, *bufP, keysz, scankey, nextkey); itemid = PageGetItemId(page, offnum); itup = (IndexTuple) PageGetItem(page, itemid); blkno = ItemPointerGetBlockNumber(&(itup->t_tid)); par_blkno = BufferGetBlockNumber(*bufP); /* * We need to save the location of the index entry we chose in the * parent page on a stack. In case we split the tree, we'll use the * stack to work back up to the parent page. We also save the actual * downlink (TID) to uniquely identify the index entry, in case it * moves right while we're working lower in the tree. See the paper * by Lehman and Yao for how this is detected and handled. (We use the * child link to disambiguate duplicate keys in the index -- Lehman * and Yao disallow duplicate keys.) */ new_stack = (BTStack) palloc(sizeof(BTStackData)); new_stack->bts_blkno = par_blkno; new_stack->bts_offset = offnum; memcpy(&new_stack->bts_btentry, itup, sizeof(IndexTupleData)); new_stack->bts_parent = stack_in; /* drop the read lock on the parent page, acquire one on the child */ *bufP = _bt_relandgetbuf(rel, *bufP, blkno, BT_READ); /* okay, all set to move down a level */ stack_in = new_stack; } return stack_in; }
/* * _bt_search() -- Search the tree for a particular scankey, * or more precisely for the first leaf page it could be on. * * Return value is a stack of parent-page pointers. *bufP is set to the * address of the leaf-page buffer, which is read-locked and pinned. * No locks are held on the parent pages, however! * * NOTE that the returned buffer is read-locked regardless of the access * parameter. However, access = BT_WRITE will allow an empty root page * to be created and returned. When access = BT_READ, an empty index * will result in *bufP being set to InvalidBuffer. */ BTStack _bt_search(Relation rel, int keysz, ScanKey scankey, Buffer *bufP, int access) { BTStack stack_in = NULL; /* Get the root page to start with */ *bufP = _bt_getroot(rel, access); /* If index is empty and access = BT_READ, no root page is created. */ if (!BufferIsValid(*bufP)) return (BTStack) NULL; /* Loop iterates once per level descended in the tree */ for (;;) { Page page; BTPageOpaque opaque; OffsetNumber offnum; ItemId itemid; BTItem btitem; IndexTuple itup; BlockNumber blkno; BlockNumber par_blkno; BTStack new_stack; /* * Race -- the page we just grabbed may have split since we read * its pointer in the parent (or metapage). If it has, we may * need to move right to its new sibling. Do that. */ *bufP = _bt_moveright(rel, *bufP, keysz, scankey, BT_READ); /* if this is a leaf page, we're done */ page = BufferGetPage(*bufP); opaque = (BTPageOpaque) PageGetSpecialPointer(page); if (P_ISLEAF(opaque)) break; /* * Find the appropriate item on the internal page, and get the * child page that it points to. */ offnum = _bt_binsrch(rel, *bufP, keysz, scankey); itemid = PageGetItemId(page, offnum); btitem = (BTItem) PageGetItem(page, itemid); itup = &(btitem->bti_itup); blkno = ItemPointerGetBlockNumber(&(itup->t_tid)); par_blkno = BufferGetBlockNumber(*bufP); /* * We need to save the location of the index entry we chose in the * parent page on a stack. In case we split the tree, we'll use * the stack to work back up to the parent page. We also save the * actual downlink (TID) to uniquely identify the index entry, in * case it moves right while we're working lower in the tree. See * the paper by Lehman and Yao for how this is detected and * handled. (We use the child link to disambiguate duplicate keys * in the index -- Lehman and Yao disallow duplicate keys.) */ new_stack = (BTStack) palloc(sizeof(BTStackData)); new_stack->bts_blkno = par_blkno; new_stack->bts_offset = offnum; memcpy(&new_stack->bts_btitem, btitem, sizeof(BTItemData)); new_stack->bts_parent = stack_in; /* drop the read lock on the parent page, acquire one on the child */ _bt_relbuf(rel, *bufP); *bufP = _bt_getbuf(rel, blkno, BT_READ); /* okay, all set to move down a level */ stack_in = new_stack; } return stack_in; }