Function DeleteOneInternal

pg_documentdb/src/commands/delete.c:1224–1531

* DeleteOneInternal deletes a single row with a specific shard key value filter. * * Returns 1 if a row was deleted, and 0 if No rows were found matching the provided query. */

 * Returns 1 if a row was deleted, and 0 if No rows were found matching the provided query.
 */
static void
DeleteOneInternal(MongoCollection *collection, DeleteOneParams *deleteOneParams,
				  int64 shardKeyHash, DeleteOneResult *result)
{
	uint64 planId = QUERY_DELETE_ONE;
	bool applyCollation = IsCollationApplicable(deleteOneParams->collationString);

	List *sortFieldDocuments = deleteOneParams->sort == NULL ? NIL :
							   BsonValueDocumentDecomposeFields(deleteOneParams->sort);
	int sortFieldDocumentsLength = list_length(sortFieldDocuments);

	int argCount = sortFieldDocumentsLength;

	bool queryHasNonIdFilters = false;
	bool isIdFilterCollationAware = false;
	pgbson *objectIdFilter =
		GetObjectIdFilterFromQueryDocumentValue(deleteOneParams->query,
												&queryHasNonIdFilters,
												&isIdFilterCollationAware);

	bool applyObjectIdFilter = objectIdFilter != NULL;
	if (applyObjectIdFilter && applyCollation)
	{
		/* if the _id filter value is collation-sensitive, we will omit */
		/* filtering by _id in the WHERE clause. */
		applyObjectIdFilter = !isIdFilterCollationAware;
	}

	argCount += applyObjectIdFilter ? 1 : 0;

	int nextSqlArgIndex = 1;
	MemoryContext outerContext = CurrentMemoryContext;

	SPI_connect();

	/*
	 * We construct a query that the distribution layer can route to a single shard, which
	 * also allows us to use LIMIT 1 and FOR UPDATE in a subquery.
	 *
	 * The LIMIT 1 ensures we only delete a single row even if there are many
	 * that match the query.
	 *
	 * The FOR UPDATE ensures that the matching row does not change or disappear
	 * concurrently. Otherwise, the DELETE might incorrectly become a noop.
	 *
	 * Note that we cannot directly place the SELECT query into the USING clause
	 * due to the reason discussed in the pgsql-bug thread:
	 * https://www.postgresql.org/message-id/3798786.1655133396%40sss.pgh.pa.us.
	 * For this reason, here we use a materialized cte to compute the ctid of the
	 * tuple that needs to be deleted.
	 */
	StringInfoData selectQuery;
	initStringInfo(&selectQuery);
	appendStringInfo(&selectQuery, "WITH s AS MATERIALIZED (SELECT ctid FROM ");

	if (collection->shardTableName[0] != '\0')
	{
		appendStringInfo(&selectQuery, " %s.%s", ApiDataSchemaName,