sql server - What is a pseudo-merge join? -

this description microsoft technet explaining trace flag 342 (emphasis added):

disables costing of pseudo-merge joins, reducing time spent on parse types of large, multi-table joins. 1 can use set forceplan on disable costing of pseudo-merge joins because query forced use order specified in clause.

does of know pseudo-merge join? far know, sql server has 3 join algorithms (nest loop join, merge join, , hash join - encompass bitmap join). pseudo-merge join, , difference between , regular merge join or other join matter?

i know kind of old question try answer specific can.

pseudo-merge not type of join used t-sql language operator, interpretation of microsoft's explanation using trace flag 342 folows:

disables costing of pseudo-merge joins, reducing time spent on parse types of large, multi-table joins.

pseudo-merge concept represent query optimiser trying calculate better query execution plan, trying obtain best way join several tables.

one can use set forceplan on disable costing of pseudo-merge joins because query forced use order specified in clause.

this option prevents optimizer trying calculate , execute joins listed in query.

an article on set forceplan on reference.