PostgreSQL 流程---插入

插入

预备知识

《PostgreSQL 基础模块—表和元组组织方式》

概述

数据库的插入操作通常是由一条Insert语句实现的。Insert语句的完整执行流程比较长，包括解析SQL语句、元组组装、元组插入等一系列流程。本章只介绍元组的组装和插入部分。元组组装与插入都在ExecInsert函数中实现，代码如下：

static TupleTableSlot *
ExecInsert(ModifyTableState *mtstate,
		   TupleTableSlot *slot,
		   TupleTableSlot *planSlot,
		   List *arbiterIndexes,
		   OnConflictAction onconflict,
		   EState *estate,
		   bool canSetTag)
{
   
   
	HeapTuple	tuple;
	ResultRelInfo *resultRelInfo;
	Relation	resultRelationDesc;
	Oid			newId;
	List	   *recheckIndexes = NIL;

	/*
	 * get the heap tuple out of the tuple table slot, making sure we have a
	 * writable copy
	 * 组装一个元组
	 */
	tuple = ExecMaterializeSlot(slot);

	/*
	 * get information on the (current) result relation
	 */
	resultRelInfo = estate->es_result_relation_info;
	resultRelationDesc = resultRelInfo->ri_RelationDesc;

	/*
	 * If the result relation has OIDs, force the tuple's OID to zero so that
	 * heap_insert will assign a fresh OID.  Usually the OID already will be
	 * zero at this point, but there are corner cases where the plan tree can
	 * return a tuple extracted literally from some table with the same
	 * rowtype.
	 *
	 * XXX if we ever wanted to allow users to assign their own OIDs to new
	 * rows, this'd be the place to do it.  For the moment, we make a point of
	 * doing this before calling triggers, so that a user-supplied trigger
	 * could hack the OID if desired.
	 */
	if (resultRelationDesc->rd_rel->relhasoids)
		HeapTupleSetOid(tuple, InvalidOid);

	/*
	 * BEFORE ROW INSERT Triggers.
	 *
	 * Note: We fire BEFORE ROW TRIGGERS for every attempted insertion in an
	 * INSERT ... ON CONFLICT statement.  We cannot check for constraint
	 * violations before firing these triggers, because they can change the
	 * values to insert.  Also, they can run arbitrary user-defined code with
	 * side-effects that we can't cancel by just not inserting the tuple.
	 */
	if (resultRelInfo->ri_TrigDesc &&
		resultRelInfo->ri_TrigDesc->trig_insert_before_row)
	{
   
   
		slot = ExecBRInsertTriggers(estate, resultRelInfo, slot);

		if (slot == NULL)		/* "do nothing" */
			return NULL;

		/* trigger might have changed tuple */
		tuple = ExecMaterializeSlot(slot);
	}

	/* INSTEAD OF ROW INSERT Triggers */
	if (resultRelInfo->ri_TrigDesc &&
		resultRelInfo->ri_TrigDesc->trig_insert_instead_row)
	{
   
   
		slot = ExecIRInsertTriggers(estate, resultRelInfo, slot);

		if (slot == NULL)		/* "do nothing" */
			return NULL;

		/* trigger might have changed tuple */
		tuple = ExecMaterializeSlot(slot);

		newId = InvalidOid;
	}
	else if (resultRelInfo->ri_FdwRoutine)
	{
   
   
		/*
		 * insert into foreign table: let the FDW do it
		 */
		slot = resultRelInfo->ri_FdwRoutine->ExecForeignInsert(estate,
															   resultRelInfo,
															   slot,
															   planSlot);

		if (slot == NULL)		/* "do nothing" */
			return NULL;

		/* FDW might have changed tuple */
		tuple = ExecMaterializeSlot(slot);

		/*
		 * AFTER ROW Triggers or RETURNING expressions might reference the
		 * tableoid column, so initialize t_tableOid before evaluating them.
		 */
		tuple->t_tableOid = RelationGetRelid(resultRelationDesc);

		newId = InvalidOid;
	}
	else
	{
   
   
		/*
		 * Constraints might reference the tableoid column, so initialize
		 * t_tableOid before evaluating them.
		 */
		tuple->t_tableOid = RelationGetRelid(resultRelationDesc);

		/*
		 * Check any RLS INSERT WITH CHECK policies
		 *
		 * ExecWithCheckOptions() will skip any WCOs which are not of the kind
		 * we are looking for at this point.
		 */
		if (resultRelInfo->ri_WithCheckOptions != NIL)
			ExecWithCheckOptions(WCO_RLS_INSERT_CHECK,
								 resultRelInfo, slot, estate);

		/*
		 * Check the constraints of the tuple
		 */
		if (resultRelationDesc->rd_att->constr)
			ExecConstraints(resultRelInfo, slot, estate);

		if (onconflict != ONCONFLICT_NONE && resultRelInfo->ri_NumIndices > 0)
		{
   
   
			/* Perform a speculative insertion. */
			uint32		specToken;
			ItemPointerData conflictTid;
			bool		specConflict;

			/*
			 * Do a non-conclusive check for conflicts first.
			 *
			 * We're not holding any locks yet, so this doesn't guarantee that
			 * the later insert won't conflict.  But it avoids leaving behind
			 * a lot of canceled speculative insertions, if you run a lot of
			 * INSERT ON CONFLICT statements that do conflict.
			 *
			 * We loop back here if we find a conflict below, either during
			 * the pre-check, or when we re-check after inserting the tuple
			 * speculatively.
			 */
	vlock:
			specConflict = false;
			if (!ExecCheckIndexConstraints(slot, estate, &conflictTid,
										   arbiterIndexes))
			{
   
   
				/* committed conflict tuple found */
				if (onconflict == ONCONFLICT_UPDATE)
				{
   
   
					/*
					 * In case of ON CONFLICT DO UPDATE, execute the UPDATE
					 * part.  Be prepared to retry if the UPDATE fails because
					 * of another concurrent UPDATE/DELETE to the conflict
					 * tuple.
					 */
					TupleTableSlot *returning = NULL;

					if (ExecOnConflictUpdate(mtstate, resultRelInfo,
											 &conflictTid, planSlot, slot,
											 estate, canSetTag, &returning))
					{
   
   
						InstrCountFiltered2(&mtstate->ps, 1);
						return returning;
					}
					else
						goto vlock;
				}
				else
				{
   
   
					/*
					 * In case of ON CONFLICT DO NOTHING, do nothing. However,
					 * verify that the tuple is visible to the executor's MVCC
					 * snapshot at higher isolation levels.
					 */
					Assert(onconflict == ONCONFLICT_NOTHING);
					ExecCheckTIDVisible(estate, resultRelInfo, &conflictTid);
					InstrCountFiltered2(&mtstate->ps, 1);
					return NULL;
				}
			}

			/*
			 * Before we start insertion proper, acquire our "speculative
			 * insertion lock".  Others can use that to wait for us to decide
			 * if we're going to go ahead with the insertion, instead of
			 * waiting for the whole transaction to complete.
			 */
			specToken = SpeculativeInsertionLockAcquire(GetCurrentTransactionId());
			HeapTupleHeaderSetSpeculativeToken(tuple->t_data, specToken);

			/* 
			 * insert the tuple, with the speculative token 
			 * 插入元组
			 */
			newId = heap_insert(resultRelationDesc, tuple,
								estate->es_output_cid,
								HEAP_INSERT_SPECULATIVE,
								NULL);

			/* insert index entries for tuple */
			recheckIndexes = ExecInsertIndexTuples(slot, &(tuple->t_self),
												 estate, true, &specConflict,
												   arbiterIndexes);

			/* adjust the tuple's state accordingly */
			if (!specConflict)
				heap_finish_speculative(resultRelationDesc, tuple);
			else
				heap_abort_speculative(resultRelationDesc, tuple);

			/*
			 * Wake up anyone waiting for our decision.  They will re-check
			 * the tuple, see that it's no longer speculative, and wait on our
			 * XID as if this was a regularly inserted tuple all along.  Or if
			 * we killed the tuple, they will see it's dead, and proceed as if
			 * the tuple never existed.
			 */
			SpeculativeInsertionLockRelease(GetCurrentTransactionId());

			/*
			 * If there was a conflict, start from the beginning.  We'll do
			 * the pre-check again, which will now find the conflicting tuple
			 * (unless it aborts before we get there).
			 */
			if (specConflict)
			{
   
   
				list_free(recheckIndexes);
				goto vlock;
			}

			/* Since there was no insertion conflict, we're done */
		}
		else
		{
   
   
			/*
			 * insert the tuple normally.
			 *
			 * Note: heap_insert returns the tid (location) of the new tuple
			 * in the t_self field.
			 * 元组插入
			 */
			newId = heap_insert(resultRelationDesc, tuple,
								estate->es_output_cid,
								0, NULL);

			/* insert index entries for tuple */
			if (resultRelInfo->ri_NumIndices > 0)
				recheckIndexes = ExecInsertIndexTuples(slot, &(tuple->t_self),
													   estate, false, NULL,
													   arbiterIndexes);
		}
	}

	if (canSetTag)
	{
   
   
		(estate->es_processed)++;
		estate->es_lastoid = newId;
		setLastTid(&(tuple->t_self));
	}

	/* AFTER ROW INSERT Triggers */
	ExecARInsertTriggers(estate, resultRelInfo, tuple, recheckIndexes);

	list_free(recheckIndexes);

	/*
	 * Check any WITH CHECK OPTION constraints from parent views.  We are
	 * required to do this after testing all constraints and uniqueness
	 * violations per the SQL spec, so we do it after actually inserting the
	 * record into the heap and all indexes.
	 *
	 * Ex