/* * index_beginscan_internal --- common code for index_beginscan variants */ static IndexScanDesc index_beginscan_internal(Relation indexRelation, int nkeys, int norderbys, Snapshot snapshot) { IndexScanDesc scan; FmgrInfo *procedure; RELATION_CHECKS; GET_REL_PROCEDURE(ambeginscan); if (!(indexRelation->rd_am->ampredlocks)) PredicateLockRelation(indexRelation, snapshot); /* * We hold a reference count to the relcache entry throughout the scan. */ RelationIncrementReferenceCount(indexRelation); /* * Tell the AM to open a scan. */ scan = (IndexScanDesc) DatumGetPointer(FunctionCall3(procedure, PointerGetDatum(indexRelation), Int32GetDatum(nkeys), Int32GetDatum(norderbys))); return scan; }
/* * index_beginscan_internal --- common code for index_beginscan variants */ static IndexScanDesc index_beginscan_internal(Relation indexRelation, int nkeys, int norderbys, Snapshot snapshot, ParallelIndexScanDesc pscan, bool temp_snap) { IndexScanDesc scan; RELATION_CHECKS; CHECK_REL_PROCEDURE(ambeginscan); if (!(indexRelation->rd_amroutine->ampredlocks)) PredicateLockRelation(indexRelation, snapshot); /* * We hold a reference count to the relcache entry throughout the scan. */ RelationIncrementReferenceCount(indexRelation); /* * Tell the AM to open a scan. */ scan = indexRelation->rd_amroutine->ambeginscan(indexRelation, nkeys, norderbys); /* Initialize information for parallel scan. */ scan->parallel_scan = pscan; scan->xs_temp_snap = temp_snap; return scan; }
/* ---------------------------------------------------------------- * ExecSeqScan(node) * * Scans the relation sequentially and returns the next qualifying * tuple. * We call the ExecScan() routine and pass it the appropriate * access method functions. * For serializable transactions, we first acquire a predicate * lock on the entire relation. * ---------------------------------------------------------------- */ TupleTableSlot * ExecSeqScan(SeqScanState *node) { PredicateLockRelation(node->ss_currentRelation); node->ss_currentScanDesc->rs_relpredicatelocked = true; return ExecScan((ScanState *) node, (ExecScanAccessMtd) SeqNext, (ExecScanRecheckMtd) SeqRecheck); }
/* * _bt_first() -- Find the first item in a scan. * * We need to be clever about the direction of scan, the search * conditions, and the tree ordering. We find the first item (or, * if backwards scan, the last item) in the tree that satisfies the * qualifications in the scan key. On success exit, the page containing * the current index tuple is pinned but not locked, and data about * the matching tuple(s) on the page has been loaded into so->currPos. * scan->xs_ctup.t_self is set to the heap TID of the current tuple, * and if requested, scan->xs_itup points to a copy of the index tuple. * * If there are no matching items in the index, we return FALSE, with no * pins or locks held. * * Note that scan->keyData[], and the so->keyData[] scankey built from it, * are both search-type scankeys (see nbtree/README for more about this). * Within this routine, we build a temporary insertion-type scankey to use * in locating the scan start position. */ bool _bt_first(IndexScanDesc scan, ScanDirection dir) { Relation rel = scan->indexRelation; BTScanOpaque so = (BTScanOpaque) scan->opaque; Buffer buf; BTStack stack; OffsetNumber offnum; StrategyNumber strat; bool nextkey; bool goback; ScanKey startKeys[INDEX_MAX_KEYS]; ScanKeyData scankeys[INDEX_MAX_KEYS]; ScanKeyData notnullkeys[INDEX_MAX_KEYS]; int keysCount = 0; int i; StrategyNumber strat_total; BTScanPosItem *currItem; pgstat_count_index_scan(rel); /* * Examine the scan keys and eliminate any redundant keys; also mark the * keys that must be matched to continue the scan. */ _bt_preprocess_keys(scan); /* * Quit now if _bt_preprocess_keys() discovered that the scan keys can * never be satisfied (eg, x == 1 AND x > 2). */ if (!so->qual_ok) return false; /*---------- * Examine the scan keys to discover where we need to start the scan. * * We want to identify the keys that can be used as starting boundaries; * these are =, >, or >= keys for a forward scan or =, <, <= keys for * a backwards scan. We can use keys for multiple attributes so long as * the prior attributes had only =, >= (resp. =, <=) keys. Once we accept * a > or < boundary or find an attribute with no boundary (which can be * thought of as the same as "> -infinity"), we can't use keys for any * attributes to its right, because it would break our simplistic notion * of what initial positioning strategy to use. * * When the scan keys include cross-type operators, _bt_preprocess_keys * may not be able to eliminate redundant keys; in such cases we will * arbitrarily pick a usable one for each attribute. This is correct * but possibly not optimal behavior. (For example, with keys like * "x >= 4 AND x >= 5" we would elect to scan starting at x=4 when * x=5 would be more efficient.) Since the situation only arises given * a poorly-worded query plus an incomplete opfamily, live with it. * * When both equality and inequality keys appear for a single attribute * (again, only possible when cross-type operators appear), we *must* * select one of the equality keys for the starting point, because * _bt_checkkeys() will stop the scan as soon as an equality qual fails. * For example, if we have keys like "x >= 4 AND x = 10" and we elect to * start at x=4, we will fail and stop before reaching x=10. If multiple * equality quals survive preprocessing, however, it doesn't matter which * one we use --- by definition, they are either redundant or * contradictory. * * Any regular (not SK_SEARCHNULL) key implies a NOT NULL qualifier. * If the index stores nulls at the end of the index we'll be starting * from, and we have no boundary key for the column (which means the key * we deduced NOT NULL from is an inequality key that constrains the other * end of the index), then we cons up an explicit SK_SEARCHNOTNULL key to * use as a boundary key. If we didn't do this, we might find ourselves * traversing a lot of null entries at the start of the scan. * * In this loop, row-comparison keys are treated the same as keys on their * first (leftmost) columns. We'll add on lower-order columns of the row * comparison below, if possible. * * The selected scan keys (at most one per index column) are remembered by * storing their addresses into the local startKeys[] array. *---------- */ strat_total = BTEqualStrategyNumber; if (so->numberOfKeys > 0) { AttrNumber curattr; ScanKey chosen; ScanKey impliesNN; ScanKey cur; /* * chosen is the so-far-chosen key for the current attribute, if any. * We don't cast the decision in stone until we reach keys for the * next attribute. */ curattr = 1; chosen = NULL; /* Also remember any scankey that implies a NOT NULL constraint */ impliesNN = NULL; /* * Loop iterates from 0 to numberOfKeys inclusive; we use the last * pass to handle after-last-key processing. Actual exit from the * loop is at one of the "break" statements below. */ for (cur = so->keyData, i = 0;; cur++, i++) { if (i >= so->numberOfKeys || cur->sk_attno != curattr) { /* * Done looking at keys for curattr. If we didn't find a * usable boundary key, see if we can deduce a NOT NULL key. */ if (chosen == NULL && impliesNN != NULL && ((impliesNN->sk_flags & SK_BT_NULLS_FIRST) ? ScanDirectionIsForward(dir) : ScanDirectionIsBackward(dir))) { /* Yes, so build the key in notnullkeys[keysCount] */ chosen = ¬nullkeys[keysCount]; ScanKeyEntryInitialize(chosen, (SK_SEARCHNOTNULL | SK_ISNULL | (impliesNN->sk_flags & (SK_BT_DESC | SK_BT_NULLS_FIRST))), curattr, ((impliesNN->sk_flags & SK_BT_NULLS_FIRST) ? BTGreaterStrategyNumber : BTLessStrategyNumber), InvalidOid, InvalidOid, InvalidOid, (Datum) 0); } /* * If we still didn't find a usable boundary key, quit; else * save the boundary key pointer in startKeys. */ if (chosen == NULL) break; startKeys[keysCount++] = chosen; /* * Adjust strat_total, and quit if we have stored a > or < * key. */ strat = chosen->sk_strategy; if (strat != BTEqualStrategyNumber) { strat_total = strat; if (strat == BTGreaterStrategyNumber || strat == BTLessStrategyNumber) break; } /* * Done if that was the last attribute, or if next key is not * in sequence (implying no boundary key is available for the * next attribute). */ if (i >= so->numberOfKeys || cur->sk_attno != curattr + 1) break; /* * Reset for next attr. */ curattr = cur->sk_attno; chosen = NULL; impliesNN = NULL; } /* * Can we use this key as a starting boundary for this attr? * * If not, does it imply a NOT NULL constraint? (Because * SK_SEARCHNULL keys are always assigned BTEqualStrategyNumber, * *any* inequality key works for that; we need not test.) */ switch (cur->sk_strategy) { case BTLessStrategyNumber: case BTLessEqualStrategyNumber: if (chosen == NULL) { if (ScanDirectionIsBackward(dir)) chosen = cur; else impliesNN = cur; } break; case BTEqualStrategyNumber: /* override any non-equality choice */ chosen = cur; break; case BTGreaterEqualStrategyNumber: case BTGreaterStrategyNumber: if (chosen == NULL) { if (ScanDirectionIsForward(dir)) chosen = cur; else impliesNN = cur; } break; } } } /* * If we found no usable boundary keys, we have to start from one end of * the tree. Walk down that edge to the first or last key, and scan from * there. */ if (keysCount == 0) return _bt_endpoint(scan, dir); /* * We want to start the scan somewhere within the index. Set up an * insertion scankey we can use to search for the boundary point we * identified above. The insertion scankey is built in the local * scankeys[] array, using the keys identified by startKeys[]. */ Assert(keysCount <= INDEX_MAX_KEYS); for (i = 0; i < keysCount; i++) { ScanKey cur = startKeys[i]; Assert(cur->sk_attno == i + 1); if (cur->sk_flags & SK_ROW_HEADER) { /* * Row comparison header: look to the first row member instead. * * The member scankeys are already in insertion format (ie, they * have sk_func = 3-way-comparison function), but we have to watch * out for nulls, which _bt_preprocess_keys didn't check. A null * in the first row member makes the condition unmatchable, just * like qual_ok = false. */ ScanKey subkey = (ScanKey) DatumGetPointer(cur->sk_argument); Assert(subkey->sk_flags & SK_ROW_MEMBER); if (subkey->sk_flags & SK_ISNULL) return false; memcpy(scankeys + i, subkey, sizeof(ScanKeyData)); /* * If the row comparison is the last positioning key we accepted, * try to add additional keys from the lower-order row members. * (If we accepted independent conditions on additional index * columns, we use those instead --- doesn't seem worth trying to * determine which is more restrictive.) Note that this is OK * even if the row comparison is of ">" or "<" type, because the * condition applied to all but the last row member is effectively * ">=" or "<=", and so the extra keys don't break the positioning * scheme. But, by the same token, if we aren't able to use all * the row members, then the part of the row comparison that we * did use has to be treated as just a ">=" or "<=" condition, and * so we'd better adjust strat_total accordingly. */ if (i == keysCount - 1) { bool used_all_subkeys = false; Assert(!(subkey->sk_flags & SK_ROW_END)); for (;;) { subkey++; Assert(subkey->sk_flags & SK_ROW_MEMBER); if (subkey->sk_attno != keysCount + 1) break; /* out-of-sequence, can't use it */ if (subkey->sk_strategy != cur->sk_strategy) break; /* wrong direction, can't use it */ if (subkey->sk_flags & SK_ISNULL) break; /* can't use null keys */ Assert(keysCount < INDEX_MAX_KEYS); memcpy(scankeys + keysCount, subkey, sizeof(ScanKeyData)); keysCount++; if (subkey->sk_flags & SK_ROW_END) { used_all_subkeys = true; break; } } if (!used_all_subkeys) { switch (strat_total) { case BTLessStrategyNumber: strat_total = BTLessEqualStrategyNumber; break; case BTGreaterStrategyNumber: strat_total = BTGreaterEqualStrategyNumber; break; } } break; /* done with outer loop */ } } else { /* * Ordinary comparison key. Transform the search-style scan key * to an insertion scan key by replacing the sk_func with the * appropriate btree comparison function. * * If scankey operator is not a cross-type comparison, we can use * the cached comparison function; otherwise gotta look it up in * the catalogs. (That can't lead to infinite recursion, since no * indexscan initiated by syscache lookup will use cross-data-type * operators.) * * We support the convention that sk_subtype == InvalidOid means * the opclass input type; this is a hack to simplify life for * ScanKeyInit(). */ if (cur->sk_subtype == rel->rd_opcintype[i] || cur->sk_subtype == InvalidOid) { FmgrInfo *procinfo; procinfo = index_getprocinfo(rel, cur->sk_attno, BTORDER_PROC); ScanKeyEntryInitializeWithInfo(scankeys + i, cur->sk_flags, cur->sk_attno, InvalidStrategy, cur->sk_subtype, cur->sk_collation, procinfo, cur->sk_argument); } else { RegProcedure cmp_proc; cmp_proc = get_opfamily_proc(rel->rd_opfamily[i], rel->rd_opcintype[i], cur->sk_subtype, BTORDER_PROC); if (!RegProcedureIsValid(cmp_proc)) elog(ERROR, "missing support function %d(%u,%u) for attribute %d of index \"%s\"", BTORDER_PROC, rel->rd_opcintype[i], cur->sk_subtype, cur->sk_attno, RelationGetRelationName(rel)); ScanKeyEntryInitialize(scankeys + i, cur->sk_flags, cur->sk_attno, InvalidStrategy, cur->sk_subtype, cur->sk_collation, cmp_proc, cur->sk_argument); } } } /*---------- * Examine the selected initial-positioning strategy to determine exactly * where we need to start the scan, and set flag variables to control the * code below. * * If nextkey = false, _bt_search and _bt_binsrch will locate the first * item >= scan key. If nextkey = true, they will locate the first * item > scan key. * * If goback = true, we will then step back one item, while if * goback = false, we will start the scan on the located item. *---------- */ switch (strat_total) { case BTLessStrategyNumber: /* * Find first item >= scankey, then back up one to arrive at last * item < scankey. (Note: this positioning strategy is only used * for a backward scan, so that is always the correct starting * position.) */ nextkey = false; goback = true; break; case BTLessEqualStrategyNumber: /* * Find first item > scankey, then back up one to arrive at last * item <= scankey. (Note: this positioning strategy is only used * for a backward scan, so that is always the correct starting * position.) */ nextkey = true; goback = true; break; case BTEqualStrategyNumber: /* * If a backward scan was specified, need to start with last equal * item not first one. */ if (ScanDirectionIsBackward(dir)) { /* * This is the same as the <= strategy. We will check at the * end whether the found item is actually =. */ nextkey = true; goback = true; } else { /* * This is the same as the >= strategy. We will check at the * end whether the found item is actually =. */ nextkey = false; goback = false; } break; case BTGreaterEqualStrategyNumber: /* * Find first item >= scankey. (This is only used for forward * scans.) */ nextkey = false; goback = false; break; case BTGreaterStrategyNumber: /* * Find first item > scankey. (This is only used for forward * scans.) */ nextkey = true; goback = false; break; default: /* can't get here, but keep compiler quiet */ elog(ERROR, "unrecognized strat_total: %d", (int) strat_total); return false; } /* * Use the manufactured insertion scan key to descend the tree and * position ourselves on the target leaf page. */ stack = _bt_search(rel, keysCount, scankeys, nextkey, &buf, BT_READ); /* don't need to keep the stack around... */ _bt_freestack(stack); /* remember which buffer we have pinned, if any */ so->currPos.buf = buf; if (!BufferIsValid(buf)) { /* * We only get here if the index is completely empty. Lock relation * because nothing finer to lock exists. */ PredicateLockRelation(rel, scan->xs_snapshot); return false; } else PredicateLockPage(rel, BufferGetBlockNumber(buf), scan->xs_snapshot); /* initialize moreLeft/moreRight appropriately for scan direction */ if (ScanDirectionIsForward(dir)) { so->currPos.moreLeft = false; so->currPos.moreRight = true; } else { so->currPos.moreLeft = true; so->currPos.moreRight = false; } so->numKilled = 0; /* just paranoia */ so->markItemIndex = -1; /* ditto */ /* position to the precise item on the page */ offnum = _bt_binsrch(rel, buf, keysCount, scankeys, nextkey); /* * If nextkey = false, we are positioned at the first item >= scan key, or * possibly at the end of a page on which all the existing items are less * than the scan key and we know that everything on later pages is greater * than or equal to scan key. * * If nextkey = true, we are positioned at the first item > scan key, or * possibly at the end of a page on which all the existing items are less * than or equal to the scan key and we know that everything on later * pages is greater than scan key. * * The actually desired starting point is either this item or the prior * one, or in the end-of-page case it's the first item on the next page or * the last item on this page. Adjust the starting offset if needed. (If * this results in an offset before the first item or after the last one, * _bt_readpage will report no items found, and then we'll step to the * next page as needed.) */ if (goback) offnum = OffsetNumberPrev(offnum); /* * Now load data from the first page of the scan. */ if (!_bt_readpage(scan, dir, offnum)) { /* * There's no actually-matching data on this page. Try to advance to * the next page. Return false if there's no matching data at all. */ if (!_bt_steppage(scan, dir)) return false; } /* Drop the lock, but not pin, on the current page */ LockBuffer(so->currPos.buf, BUFFER_LOCK_UNLOCK); /* OK, itemIndex says what to return */ currItem = &so->currPos.items[so->currPos.itemIndex]; scan->xs_ctup.t_self = currItem->heapTid; if (scan->xs_want_itup) scan->xs_itup = (IndexTuple) (so->currTuples + currItem->tupleOffset); return true; }
/* * _bt_endpoint() -- Find the first or last page in the index, and scan * from there to the first key satisfying all the quals. * * This is used by _bt_first() to set up a scan when we've determined * that the scan must start at the beginning or end of the index (for * a forward or backward scan respectively). Exit conditions are the * same as for _bt_first(). */ static bool _bt_endpoint(IndexScanDesc scan, ScanDirection dir) { Relation rel = scan->indexRelation; BTScanOpaque so = (BTScanOpaque) scan->opaque; Buffer buf; Page page; BTPageOpaque opaque; OffsetNumber start; BTScanPosItem *currItem; /* * Scan down to the leftmost or rightmost leaf page. This is a simplified * version of _bt_search(). We don't maintain a stack since we know we * won't need it. */ buf = _bt_get_endpoint(rel, 0, ScanDirectionIsBackward(dir)); if (!BufferIsValid(buf)) { /* * Empty index. Lock the whole relation, as nothing finer to lock * exists. */ PredicateLockRelation(rel, scan->xs_snapshot); so->currPos.buf = InvalidBuffer; return false; } PredicateLockPage(rel, BufferGetBlockNumber(buf), scan->xs_snapshot); page = BufferGetPage(buf); opaque = (BTPageOpaque) PageGetSpecialPointer(page); Assert(P_ISLEAF(opaque)); if (ScanDirectionIsForward(dir)) { /* There could be dead pages to the left, so not this: */ /* Assert(P_LEFTMOST(opaque)); */ start = P_FIRSTDATAKEY(opaque); } else if (ScanDirectionIsBackward(dir)) { Assert(P_RIGHTMOST(opaque)); start = PageGetMaxOffsetNumber(page); } else { elog(ERROR, "invalid scan direction: %d", (int) dir); start = 0; /* keep compiler quiet */ } /* remember which buffer we have pinned */ so->currPos.buf = buf; /* initialize moreLeft/moreRight appropriately for scan direction */ if (ScanDirectionIsForward(dir)) { so->currPos.moreLeft = false; so->currPos.moreRight = true; } else { so->currPos.moreLeft = true; so->currPos.moreRight = false; } so->numKilled = 0; /* just paranoia */ so->markItemIndex = -1; /* ditto */ /* * Now load data from the first page of the scan. */ if (!_bt_readpage(scan, dir, start)) { /* * There's no actually-matching data on this page. Try to advance to * the next page. Return false if there's no matching data at all. */ if (!_bt_steppage(scan, dir)) return false; } /* Drop the lock, but not pin, on the current page */ LockBuffer(so->currPos.buf, BUFFER_LOCK_UNLOCK); /* OK, itemIndex says what to return */ currItem = &so->currPos.items[so->currPos.itemIndex]; scan->xs_ctup.t_self = currItem->heapTid; if (scan->xs_want_itup) scan->xs_itup = (IndexTuple) (so->currTuples + currItem->tupleOffset); return true; }