Execution Plan basics for developers

I have said this before. I expect the developers to only do basic tuning. But they do need to know a bit about this complex tool. What is this tool? It comes in 3 flavors. And it is house SQL Server decides how to make the query run and fast as possible that. Remember, SQL Server has an extremely short time to make choices and allow a query to run. In the moments between hitting execute and displaying the results. But in detail, here are the steps.

The query is parsed to verify it will run. Yes, reject the flawed queries as quick as
The code is sent to the Algebrator to have the data types and names within the
The query processor tree gets the This is where the fun begins. A hash is generated and compared against the plan cache. If found, it runs with the plan. Otherwise, it creates a plan. This introduces the possibility of parameter sniffing. If your query runs fast today and slow tomorrow, then check your stats and look into parameter sniffing. A lot of the time, this means you might contact your DBA to help solve the issue. This parameter sniffing concept is worthy of taking a formal class on if you are really interested in tuning queries.
The query optimizer first decides what it thinks the most efficient plan. This is based on the statistics. Plan creating costs a lot of time. Given this time to build a new plan, sometimes the sub-optimal plan is the more efficient plan. This efficiency concept is based on i/o and CPU for each operation to deliver the results set.

The three flavors of plans.

Live Execution plan
Estimated, this is a quick
Actual Execution plan

Execution plan screen layout

Header

Cost
Query text
Missing indexes (guess)

Graphical view of Operators (icons) and flow control (arrows)

Icons

There is a log of icons, and I will describe them in detail down in a minute or so. More importantly for developers is the indicators. I call them badges it matches smartphone application development more.

Indicators

These are simple like badges on your smartphone added to an icon. These badges come in two types currently.

Operator Warning – The query was so badly estimated that it spilled to
Parallel Indicator – The query went This is good and bad good if it parallels evenly, and that is all that is needed.

The arrows do have meaning. Arrow 1 is processing a few rows of data. Arrow 2 is a lot of data.

The thicker the arrow, the more data that is being processed.

If you hover over any object, you will get a list of properties. In the example above, with the arrows, it will tell you the actual number of rows, the number of rows read, the estimated number of rows, estimated row sizes and estimated data size.

What are all these operator icons?

Each operator has properties, and Microsoft lists them willy-nilly and unordered! Download the Cheat Sheet

Image	Operator	Description
Enhancers/Badges
	Parallelism	The Parallelism operator (or Exchange Iterator) performs the distribution streams, gather streams, and repartition streams logical operations. The Argument columns can contain a PARTITION COLUMNS:() predicate with a comma-separated list of the columns being partitioned. The Argument columns can also contain an ORDER BY:() predicate, listing the columns to preserve the sort order for during partitioning. Parallelism is a physical operator. For more information about the Parallelism operator, see Craig Freedman’s blog series. Note: If a query has been compiled as a parallel query, but at run time it is run as a serial query, the Showplan output generated by SET STATISTICS XML or by using the Include Actual Execution Plan option in SQL Server Management Studio will not contain the RunTimeInformation element for the Parallelism operator. In SET STATISTICS PROFILE output, the actual row counts and an actual number of executes will display zeroes for the Parallelism operator. When either condition occurs, it means that the Parallelism operator was only used during query compilation and not in the run-time query plan. Note that sometimes parallel query plans are run in serial if there is a high concurrent load on the server.
	Warning	Warning
	Spool	Spool to TempDb and possibly disk
	Delete	Delete operation
	Merge	Merge Operation
	Update	Update Operation
Table
	Result	The Result operator is the data returned at the end of a query plan. This is usually the root element of a Showplan. The result is a language element.
	Top	The Top operator scans the input, returning only the first specified number or percent of rows, possibly based on sort order. The Argument column can contain a list of the columns that are being checked for ties. In update plans, the Top operator is used to enforce row count limits. The top is a logical and physical operator.
	Constant Scan	The Constant Scan operator introduces one or more constant rows into a query. A Compute Scalar operator is often used after a Constant Scan to add columns to a row produced by the Constant Scan operator.
	Parameter Table Scan	The Parameter Table Scan operator scans a table that is acting as a parameter in the current query. Typically, this is used for INSERT queries within a stored procedure. Parameter Table Scan is a logical and physical operator.
	Remote Scan	The Remote Scan operator scans a remote object. The name of the remote object appears in the Argument column. Remote Scan is a logical and physical operator.
	Table Scan	The Table Scan operator retrieves all rows from the table specified in the Argument column of the query execution plan. If a WHERE:() predicate appears in the Argument column, only those rows that satisfy the predicate are returned. Table Scan is a logical and physical operator.
	Sort	The Sort operator sorts all incoming rows. The Argument column contains either a DISTINCT ORDER BY:() predicate if duplicates are removed by this operation, or an ORDER BY:() predicate with a comma-separated list of the columns being sorted. The columns are prefixed with the value ASC if the columns are sorted in ascending order or the value DESC if the columns are sorted in descending order. Sort is a logical and physical operator.
	Insert	The Insert logical operator inserts each row from its input into the object specified in the Argument column. The physical operator is either the Table Insert, Index Insert, or Clustered Index Insert operator.
	Remote Insert	The Remote Insert operator inserts the input rows into a remote object. Remote Insert is a logical and physical operator.
	Table Insert	The Table Insert operator inserts rows from its input into the table specified in the Argument column of the query execution plan. The Argument column also contains a SET:() predicate, which indicates the value to which each column is set. If Table Insert has no children for insert values, then the row inserted is taken from the Insert operator itself. Table Insert is a physical operator.
	Inserted Scan	The Inserted Scan operator scans the inserted table. Inserted Scan is a logical and physical operator.
	Table Merge	The Table Merge operator applies a merge data stream to a heap. The operator deletes, updates, or inserts rows in the table specified in the Argument column of the operator. The actual operation performed depends on the run-time value of the ACTION column specified in the Argument column of the operator. Table Merge is a physical operator.
	Table Update	The Table Update physical operator updates input rows in the table specified in the Argument column of the query execution plan. The SET:() predicate determines the value of each updated column. These values may be referenced in the SET clause or elsewhere within this operator as well as elsewhere within this query.
	Remote Update	The Remote Update operator updates the input rows in a remote object. Remote Update is a logical and physical operator.
	Update	The Update operator updates each row from its input in the object specified in the Argument column of the query execution plan. The update is a logical operator. The physical operator is Table Update, Index Update, or Clustered Index Update.
	Delete	The Delete operator deletes from object rows that satisfy the optional predicate in the Argument column.
	Deleted Scan	The Deleted Scan operator scans the deleted table within a trigger.
	Remote Delete	The Remote Delete operator deletes the input rows from a remote object. Remote Delete is a logical and physical operator.
	Table Delete	The Table Delete physical operator deletes rows from the table specified in the Argument column of the query execution plan.
	Compute Scalar	The Compute Scalar operator evaluates an expression to produce a computed scalar value. This may then be returned to the user, referenced elsewhere in the query, or both. An example of both is in a filter predicate or join predicate. Compute Scalar is a logical and physical operator. Compute Scalar operators that appear in Showplans generated by SET STATISTICS XML might not contain the RunTime Information element. In graphical Showplans, Actual Rows, Actual Rebinds, and Actual Rewinds might be absent from the Properties window when the Include Actual Execution Plan option is selected in SQL Server Management Studio. When this occurs, it means that although these operators were used in the compiled query plan, their work was performed by other operators in the run-time query plan. Also, note that the number of executes in Showplan output generated by SET STATISTICS PROFILE is equivalent to the sum of rebinds and rewinds in Showplans generated by SET STATISTICS XML.
	Table-valued Function	The Table-valued Function operator evaluates a table-valued function (either Transact-SQL or CLR) and stores the resulting rows in the tempdb database. When the parent iterators request the rows, the Table-valued Function returns the rows from tempdb. Queries with calls to table-valued functions generate query plans with the Table-valued Function iterator. Table-valued Function can be evaluated with different parameter values: -Table-valued Function XML Reader inputs an XML BLOB as a parameter and produces a rowset representing XML nodes in XML document order. Other input parameters may restrict XML nodes returned to a subset of XML document. -Table-Valued Function XML Reader with XPath filter is a special type of XML Reader Table-valued Function that restricts output to XML nodes satisfying an XPath expression. Table-valued Function is a logical and physical operator.
	Split	The Split operator is used to optimize update processing. It splits each update operation into a delete and an insert operation. Split is a logical and physical operator.
	Segment	A segment is a physical and a logical operator. It divides the input set into segments based on the value of one or more columns. These columns are shown as arguments in the Segment operator. The operator then outputs one segment at a time.
	Sequence	The Sequence operator drives wide update plans. Functionally, it executes each input in sequence (top to bottom). Each input is usually an update of a different object. It returns only those rows that come from its last (bottom) input. A sequence is a logical and physical operator.
	Sequence Project	The Sequence Project operator adds columns to perform computations over an ordered set. It divides the input set into segments based on the value of one or more columns. The operator then outputs one segment at a time. These columns are shown as arguments in the Sequence Project operator. Sequence Project is a logical and physical operator.
None	Top N Sort	Top N Sort is similar to the Sort iterator, except that only the first N rows are needed and not the entire result set. For small values of N, the SQL Server query execution engine attempts to perform the entire sort operation in memory. For large values of N, the query execution engine resorts to the more generic method of sorting, to which N is not a parameter.
None	Distinct	The Distinct operator removes duplicates from a rowset or from a collection of values. Distinct is a logical operator.
None	Distinct Sort	The Distinct Sort logical operator scans the input, removing duplicates and sorting by the columns specified in the DISTINCT ORDER BY:() predicate of the Argument column. Distinct Sort is a logical operator.
None	Flow Distinct	The Flow Distinct logical operator scans the input, removing duplicates. Whereas the Distinct operator consumes all input before producing any output, the Flow Distinct operator returns each row as it is obtained from the input (unless that row is a duplicate, in which case it is discarded).
	Window Spool	The Window Spool operator expands each row into the set of rows that represents the window associated with it. In a query, the OVER clause defines the window within a query result set, and a window function then computes a value for each row in the window. Window Spool is a logical and physical operator.
Index
	Index Insert	The Index Insert operator inserts rows from its input into the nonclustered index specified in the Argument column. The Argument column also contains a SET:() predicate, which indicates the value to which each column is set. Index Insert is a physical operator.
	Nonclustered Index Delete	The Nonclustered Index Delete operator deletes input rows from the nonclustered index specified in the Argument column. Nonclustered Index Delete is a physical operator.
	Clustered Index Delete	The Clustered Index Delete operator deletes rows from the clustered index specified in the Argument column of the query execution plan. If a WHERE:() predicate is present in the Argument column, then only those rows that satisfy the predicate are deleted. Clustered Index Delete is a physical operator.
	Clustered Index Insert	The Clustered Index Insert Showplan operator inserts rows from its input into the clustered index specified in the Argument column. The Argument column also contains a SET:() predicate, which indicates the value to which each column is set. If Clustered Index Insert has no children for insert values, the row inserted is taken from the Insert operator itself. Clustered Index Insert is a physical operator.
	Online Index Insert	The Online Index Insert physical operator indicates that an index creates, alter, or drop operation is performed online. That is, the underlying table data remains available to users during the index operation.
	Nonclustered Index Update	The Nonclustered Index Update physical operator updates rows from its input in the nonclustered index specified in the Argument column. If a SET:() predicate is present, each updated column is set to this value. Nonclustered Index Update is a physical operator.
	Clustered Index Merge	The Clustered Index Merge operator applies a merge data stream to a clustered index. The operator deletes, updates, or inserts rows from the clustered index specified in the Argument column of the operator. The actual operation performed depends on the runtime value of the ACTION column specified in the Argument column of the operator. Clustered Index Merge is a physical operator.
	Clustered Index Update	The Clustered Index Update operator updates input rows in the clustered index specified in the Argument column.If a WHERE:() predicate is present, only those rows that satisfy this predicate are updated. If a SET:() predicate is present, each updated column is set to this value. If a DEFINE:() predicate is present, the values that this operator defines are listed. These values may be referenced in the SET clause or elsewhere within this operator and elsewhere within this query. Clustered Index Update is a logical and physical operator.
	Index Spool	The Index Spool physical operator contains a SEEK:() predicate in the Argument column. The Index Spool operator scans its input rows, placing a copy of each row in a hidden spool file (stored in the tempdb database and existing only for the lifetime of the query), and builds a nonclustered index on the rows. This allows you to use the seeking capability of indexes to output only those rows that satisfy the SEEK:() predicate. If the operator is rewound (for example, by a Nested Loops operator) but no rebinding is needed, the spooled data is used instead of rescanning the input.
	Index Seek	The Index Seek operator uses the seeking ability of indexes to retrieve rows from a nonclustered index. The Argument column contains the name of the nonclustered index being used. It also contains the SEEK:() predicate. The storage engine uses the index to process only those rows that satisfy the SEEK:() predicate. It optionally may include a WHERE:() predicate, which the storage engine will evaluate against all rows that satisfy the SEEK:() predicate (it does not use the indexes to do this). If the Argument column contains the ORDERED clause, the query processor has determined that the rows must be returned in the order in which the nonclustered index has sorted them. If the ORDERED clause is not present, the storage engine searches the index in the optimal way (which does not guarantee that the output will be sorted). Allowing the output to retain its ordering may be less efficient than producing nonsorted output. Index Seek is a logical and physical operator.
	Remote Index Seek	The Remote Index Seek operator uses the seeking ability of a remote index object to retrieve rows. The Argument column contains the name of the remote index being used and the SEEK:() predicate. Remote Index Seek is a logical, physical operator.
	Clustered Index Seek	The Clustered Index Seek operator uses the seeking ability of indexes to retrieve rows from a clustered index. The Argument column contains the name of the clustered index being used and the SEEK:() predicate. The storage engine uses the index to process only those rows that satisfy this SEEK:() predicate. It can also include a WHERE:() predicate where the storage engine evaluates against all rows that satisfy the SEEK:() predicate, but this is optional and does not use indexes to complete this process. If the Argument column contains the ORDERED clause, the query processor has determined that the rows must be returned in the order in which the clustered index has sorted them. If the ORDERED clause is not present, the storage engine searches the index in an optimal way without necessarily sorting the output. Allowing the output to retain its ordering can be less efficient than producing nonsorted output. When the keyword LOOKUP appears, then a bookmark lookup is being performed. In SQL Server 2008 and later versions, the Key Lookup operator provides bookmark lookup functionality. Clustered Index Seek is a logical and physical operator.
	Index Scan	The Index Scan operator retrieves all rows from the nonclustered index specified in the Argument column. If an optional WHERE:() predicate appears in the Argument column, only those rows that satisfy the predicate are returned. Index Scan is a logical and physical operator.
	Remote Index Scan	The Remote Index Scan operator scans the remote index specified in the Argument column. Remote Index Scan is a logical and physical operator.
	Clustered Index Scan	The Clustered Index Scan operator scans the clustered index specified in the Argument column of the query execution plan. When an optional WHERE:() predicate is present, only those rows that satisfy the predicate are returned. If the Argument column contains the ORDERED clause, the query processor has requested that the output of the rows be returned in the order in which the clustered index has sorted it. If the ORDERED clause is not present, the storage engine scans the index in an optimal way without necessarily sorting the output. Clustered Index Scan is a logical and physical operator.
	Columnstore Index Scan	The Columnstore Index Scan operator scans the column store index specified in the Argument column of the query execution plan.
Joins
	Adaptive Join	The Adaptive Join operator enables the choice of a hash join or nested loops to join method to be deferred until after the first input has been scanned. The Adaptive Join operator is a physical operator. For more information, see Understanding Adaptive joins.
None	Left Anti Semi Join	The Left Anti Semi Join operator returns each row from the first (top) input when there is no matching row in the second (bottom) input. If no join predicate exists in the Argument column, each row is a matching row. Left Anti-Semi Join is a logical operator.
None	Left Outer Join	The Left Outer Join operator returns each row that satisfies the join of the first (top) input with the second (bottom) input. It also returns any rows from the first input that had no matching rows in the second input. The nonmatching rows in the second input are returned as null values. If no join predicate exists in the Argument column, each row is a matching row. Left Outer Join is a logical operator.
None	Left Semi Join	The Left Semi Join operator returns each row from the first (top) input when there is a matching row in the second (bottom) input. If no join predicate exists in the Argument column, each row is a matching row. Left Semi Join is a logical operator.
None	Cross Join	The Cross Join operator joins each row from the first (top) input with each row from the second (bottom) input. Cross Join is a logical operator.
None	Full Outer Join	The Full Outer Join logical operator returns each row satisfying the join predicate from the first (top) input joined with each row from the second (bottom) input. It also returns rows from: -The first input had no matches in the second input. -The second input had no matches in the first input. The input that does not contain the matching values is returned as a null value. Full Outer Join is a logical operator.
None	Inner Join	The Inner Join logical operator returns each row that satisfies the join of the first (top) input with the second (bottom) input.
	Merge Join	The Merge Join operator performs the inner join, left outer join, left semi-join, left anti semi to join, right outer join, right semi-join, right anti semi join, and union logical operations. In the Argument column, the Merge Join operator contains a MERGE:() predicate if the operation is performing a one-to-many join or a MANY-TO-MANY MERGE:() predicate if the operation is performing a many-to-many join. The Argument column also includes a comma-separated list of columns used to perform the operation. The Merge Join operator requires two inputs sorted on their respective columns, possibly by inserting explicit sort operations into the query plan. Merge join is particularly effective if explicit sorting is not required, for example, if there is a suitable B-tree index in the database or if the sort order can be exploited for multiple operations, such as a merge join and grouping with a roll-up. Merge Join is a physical operator. For more information, see Understanding Merge joins.
None	Right Anti Semi Join	The Right Anti Semi Join operator outputs each row from the second (bottom) input when a matching row in the first (top) input does not exist. A matching row is defined as a row that satisfies the predicate in the Argument column (if no predicate exists, each row is a matching row). Right, Anti Semi Join is a logical operator.
None	Right Outer Join	The Right Outer Join operator returns each row that satisfies the join of the second (bottom) input with each matching row from the first (top) input. It also returns any rows from the second input that had no matching rows in the first input, joined with NULL. If no join predicate exists in the Argument column, each row is a matching row. Right, Outer Join is a logical operator.
None	Right Semi Join	The Right Semi Join operator returns each row from the second (bottom) input when there is a matching row in the first (top) input. If no join predicate exists in the Argument column, each row is a matching row. Right, Semi Join is a logical operator.
None	Union	The Union operator scans multiple inputs, outputting each row scanned and removing duplicates. Union is a logical operator.
	Concatenation	The Concatenation operator scans multiple inputs, returning each row scanned. Concatenation is typically used to implement the Transact-SQL UNION ALL construct. The Concatenation physical operator has two or more inputs and one output. Concatenation copies rows from the first input stream to the output stream then repeats this operation for each additional input stream. Concatenation is a logical and physical operator.
	Bitmap Create	The Bitmap Create operator appears in the Showplan output where bitmaps are built. Bitmap Create is a logical operator.
	Bitmap	SQL Server uses the Bitmap operator to implement bitmap filtering in parallel query plans. Bitmap filtering speeds up query execution by eliminating rows with key values that cannot produce any join records before passing rows through another operator, such as the Parallelism operator. A bitmap filter uses a compact representation of a set of values from a table in one part of the operator tree to filter rows from a second table in another part of the tree. By removing unnecessary rows early in the query, subsequent operators have fewer rows to work with, and the overall performance of the query improves. The optimizer determines when a bitmap is selective enough to be useful and in which operators to apply the filter. A bitmap is a physical operator.
TempDB
	Spool	The Spool operator saves an intermediate query result to the tempdb database.
	Lazy Spool	The Lazy Spool logical operator stores each row from its input in a hidden temporary object stored in the tempdb database. If the operator is rewound (for example, by a Nested Loops operator) but no rebinding is needed, the spooled data is used instead of rescanning the input. If rebinding is needed, the spooled data is discarded, and the spool object is rebuilt by rescanning the (rebound) input. The Lazy Spool operator builds its spool file in a “lazy” manner. That is, each time the spool’s parent operator asks for a row, the spool operator gets a row from its input operator and stores it in the spool, rather than consuming all rows at once. Lazy Spool is a logical operator.
	Eager Spool	The Eager Spool operator takes the entire input, storing each row in a hidden temporary object stored in the tempdb database. If the operator is rewound (for example, by a Nested Loops operator) but no rebinding is needed, the spooled data is used instead of rescanning the input. If rebinding is needed, the spooled data is discarded, and the spool object is rebuilt by rescanning the (rebound) input. The Eager Spool operator builds its spool file in an “eager” manner: when the spool’s parent operator asks for the first row, the spool operator consumes all rows from its input operator and stores them in the spool. Eager Spool is a logical operator.
	Table Spool	The Table Spool operator scans the input and places a copy of each row in a hidden spool table that is stored in the tempdb database and existing only for the lifetime of the query. If the operator is rewound (for example, by a Nested Loops operator) but no rebinding is needed, the spooled data is used instead of rescanning the input. Table Spool is a physical operator.
	Index Spool	The Index Spool physical operator contains a SEEK:() predicate in the Argument column. The Index Spool operator scans its input rows, placing a copy of each row in a hidden spool file (stored in the tempdb database and existing only for the lifetime of the query), and builds a nonclustered index on the rows. This allows you to use the seeking capability of indexes to output only those rows that satisfy the SEEK:() predicate. If the operator is rewound (for example, by a Nested Loops operator) but no rebinding is needed, the spooled data is used instead of rescanning the input.
Flow
	Filter	The Filter operator scans the input, returning only those rows that satisfy the filter expression (predicate) that appears in the Argument column.
	Collapse	The Collapse operator optimizes update processing. When an update is performed, it can be split (using the Split operator) into a delete and an insert. The Argument column contains a GROUP BY:() clause that specifies a list of key columns. If the query processor encounters adjacent rows that delete and insert the same key values, it replaces these separate operations with a single more efficient update operation. Collapse is a logical and physical operator.
	Dynamic	The Dynamic operator uses a cursor that can see all changes made by others.
	Keyset	The Keyset operator uses a cursor that can see updates but not inserts made by others.
	Snapshot	The Snapshot operator creates a cursor that does not see changes made by others.
	Fetch Query	The Fetch Query operator retrieves rows when a fetch is issued against a cursor.
	Population Query	The Population Query operator populates the worktable of a cursor when the cursor is opened.
	Refresh Query	The Refresh Query operator fetches current data for rows in the fetch buffer.
	Remote Query	The Remote Query operator submits a query to a remote source. The text of the query sent to the remote server appears in the Argument column. Remote Query is a logical and physical operator.
	Assert	The Assert operator verifies a condition. For example, it validates referential integrity or ensures that a scalar subquery returns one row. For each input row, the Assert operator evaluates the expression in the Argument column of the execution plan. If this expression evaluates to NULL, the row is passed through the Assert operator, and the query execution continues. If this expression evaluates to a non-null value, the appropriate error will be raised. The Assert operator is a physical operator.
	Gather Streams	The Gather Streams operator is only used in parallel query plans. The Gather Streams operator consumes several input streams and produces a single output stream of records by combining the input streams. The record contents and format are not changed. If this operator is order-preserving, all input streams must be ordered. If the output is ordered, the Argument column contains an ORDER BY:() predicate and the names of columns being ordered. Gather Streams is a logical operator.
	Distribute Streams	The Distribute Streams operator is used only in parallel query plans. The Distribute Streams operator takes a single input stream of records and produces multiple output streams. The record contents and format are not changed. Each record from the input stream appears in one of the output streams. This operator automatically preserves the relative order of the input records in the output streams. Usually, hashing is used to decide to which output stream a particular input record belongs. If the output is partitioned, then the Argument column contains a PARTITION COLUMNS:() predicate and the partitioning columns. Distribute Streams is a logical operator
	Repartition Streams	The Repartition Streams operator (or exchange iterator) consumes multiple streams and produces multiple streams of records. The record contents and format are not changed. If the query optimizer uses a bitmap filter, the number of rows in the output stream is reduced. Each record from an input stream is placed into one output stream. If this operator is order-preserving, all input streams must be ordered and merged into several ordered output streams. If the output is partitioned, the Argument column contains a PARTITION COLUMNS:() predicate and the partitioning columns. If the output is ordered, the Argument column contains an ORDER BY:() predicate and the columns being ordered. Repartition Streams is a logical operator. The operator is used only in parallel query plans.
	Merge Interval	The Merge Interval operator merges multiple (potentially overlapping) intervals to produce minimal, nonoverlapping intervals that are then used to seek index entries. This operator typically appears above one or more Compute Scalar operators over Constant Scan operators, which construct the intervals (represented as columns in a row) that this operator merges. Merge Interval is a logical and physical operator.
	While	The While operator implements the Transact-SQL while loop. While it is a language element
	Nested Loops	The Nested Loops operator performs the inner join, left outer join, left semi-join, and left anti semi to join logical operations. Nested loop joins perform a search on the inner table for each row of the outer table, typically using an index. The query processor decides, based on anticipated costs, whether to sort the outer input in order to improve the locality of the searches on the index over the inner input. Any rows that satisfy the (optional) predicate in the Argument column are returned as applicable, based on the logical operation being performed. When the OPTIMIZED attribute is set to True, it means that an Optimized Nested Loops (or Batch Sort) is used. Nested Loop is a physical operator. For more information, see Understanding Nested Loops joins.
	Row Count Spool	The Row Count Spool operator scans the input, counting how many rows are present and returning the same number of rows without any data in them. This operator is used when it is important to check for the existence of rows rather than the data contained in the rows. For example, if a Nested Loops operator performs a left semi join operation, and the join predicate applies to inner input, a row count spool may be placed at the top of the inner input of the Nested Loops operator. Then the Nested Loops operator can determine how many rows are output by the row count spool (because the actual data from the inner side is not needed) to determine whether to return the outer row. Row Count Spool is a physical operator.
	Convert	The Convert operator converts one scalar data type to another. Convert is a language element.
	catchall	The catchall icon is displayed when a suitable icon for the iterator cannot be found by the logic that produces graphical showplans. The catchall icon does not necessarily indicate an error condition. There are three catchall icons: blue (for iterators), orange (for cursors), and green (for Transact-SQL language elements).
	If	The If operator carries out conditional processing based on an expression. It is a language element.
	Switch	The switch is a special type of concatenation iterator that has n inputs. An expression is associated with each Switch operator. Depending on the return value of the expression (between 0 and n-1), Switch copies the appropriate input stream to the output stream. One use of Switch is to implement query plans involving fast forward cursors with certain operators such as the TOP operator. The switch is both a logical and physical operator.
	Intrinsic	The Intrinsic operator invokes an internal Transact-SQL function. Intrinsic is a language element.
	Iterator	The Iterator catchall icon is displayed when a suitable icon for the iterator cannot be found by the logic that produces graphical Showplans. The catchall icon does not necessarily indicate an error condition. There are three catchall icons: blue (for iterators), orange (for cursors), and green (for Transact-SQL language constructs).
	Language Element	The Language Element catchall icon is displayed when a suitable icon for the iterator cannot be found by the logic that produces graphical Showplans. The catchall icon does not necessarily indicate an error condition. There are three catchall icons: blue (for iterators), orange (for cursors), and green (for Transact-SQL language constructs).
	RID Lookup	RID Lookup is a bookmark lookup on a heap using a supplied row identifier (RID). The Argument column contains the bookmark label used to look up the row in the table and the name of the table in which the row is looked up. RID Lookup is always accompanied by a NESTED LOOP JOIN. RID Lookup is a physical operator. For more information about bookmark lookups, see “Bookmark Lookup” on the MSDN SQL Server blog.
	Stream Aggregate	The Stream Aggregate operator groups rows by one or more columns and then calculates one or more aggregate expressions returned by the query. The output of this operator can be referenced by later operators in the query, returned to the client, or both. The Stream Aggregate operator requires input ordered by the columns within its groups. The optimizer will use a Sort operator prior to this operator if the data is not already sorted due to a prior Sort operator or due to an ordered index seek or scan. In the SHOWPLAN_ALL statement or the graphical execution plan in SQL Server Management Studio, the columns in the GROUP BY predicate are listed in the Argument column, and the aggregate expressions are listed in the Defined Values column. Stream Aggregate is a physical operator.
	Log Row Scan	The Log Row Scan operator scans the transaction log. Log Row Scan is a logical and physical operator.
	Build Hash	Indicates the build of a batch hash table for an xVelocity memory optimized column store index.
	Hash Match	The Hash Match operator builds a hash table by computing a hash value for each row from its build input. A HASH:() predicate with a list of columns used to create a hash value appears in the Argument column. Then, for each probe row (as applicable), it computes a hash value (using the same hash function) and looks in the hash table for matches. If a residual predicate is present (identified by RESIDUAL:() in the Argument column), that predicate must also be satisfied for rows to be considered a match. Behavior depends on the logical operation being performed: -For any joins, use the first (top) input to build the hash table and the second (bottom) input to probe the hash table—output matches (or nonmatches) as dictated by the join type. If multiple joins use the same join column, these operations are grouped into a hash team. -For the distinct or aggregate operators, use the input to build the hash table (removing duplicates and computing any aggregate expressions). When the hash table is built, scan the table and output all entries. -For the union operator, use the first input to build the hash table (removing duplicates). Use the second input (which must have no duplicates) to probe the hash table, returning all rows that have no matches, then scan the hash table and return all entries. Hash Match is a physical operator. For more information, see Understanding Hash joins.
	Foreign Key References Check	The Foreign Key References Check operator performs referential integrity checks in place by comparing the modified row to the rows in the referencing tables to verify that the modification will not break the referential integrity. The Foreign Key References Check operator is used when more than 253 foreign key references exist on the same primary or unique key. Foreign Key References Check is a logical and physical operator.
None	Cursor	The Cursor logical and physical operators are used to describe how a query or update involving cursor operations is executed. The physical operators describe the physical implementation algorithm used to process the cursor, for example, using a keyset-driven cursor. Each step in the execution of a cursor involves a physical operator. The logical operators describe a property of the cursor, such as the cursor is read-only. Logical operators include Asynchronous, Optimistic, Primary, Read Only, Scroll Locks, and Secondary and Synchronous. Physical operators include Dynamic, Fetch Query, Keyset, Population Query, Refresh Query, and Snapshot.
	Key Lookup	The Key Lookup operator is a bookmark lookup on a table with a clustered index. The Argument column contains the name of the clustered index and the clustering key used to look up the row in the clustered index. Key Lookup is always accompanied by a Nested Loops operator. If the WITH PREFETCH clause appears in the Argument column, the query processor has determined that it is optimal to use asynchronous prefetching (read-ahead) when looking up bookmarks in the clustered index. The use of a Key Lookup operator in a query plan indicates that the query might benefit from performance tuning. For example, query performance might be improved by adding a covering index.
	Bookmark Lookup	The Bookmark Lookup operator uses a bookmark (row ID or clustering key) to look up the corresponding row in the table or clustered index. The Argument column contains the bookmark label used to look up the row in the table or clustered index. The Argument column also contains the name of the table or clustered index in which the row is looked up. If the WITH PREFETCH clause appears in the Argument column, the query processor has determined that it is optimal to use asynchronous prefetching (read-ahead) when looking up bookmarks in the table or clustered index. Starting with SQL Server 2005 (9.x), Bookmark Lookup is not used. Instead, Key Lookup and RID Lookup provide bookmark lookup functionality.
None	Async Concat	The Async Concat operator is used only in remote queries (distributed queries). It has n children and one parent node. Usually, some of the children are remote computers that participate in a distributed query. Async Concat issues open() calls to all of the children simultaneously and then apply a bitmap to each child. For each bit that is a 1, Async Concat sends the output rows to the parent node on demand.
None	Aggregate	The Aggregate operator calculates an expression containing MIN, MAX, SUM, COUNT, or AVG. The Aggregate operator can be a logical operator or a physical operator.
None	Cache	The cache is a specialized version of the Spool operator. It stores only one row of data. The cache is a logical operator. The cache is not used in SQL Server 2019 (15.x).
None	Broadcast	Broadcast has one child node and n parent node. Broadcast sends its input rows to multiple consumers on demand. Each consumer gets all of the rows. For example, if all of the consumers are build sides of a hash join, then n copies of the hash tables will be built.
None	Partial Aggregate	Partial Aggregate is used in parallel plans. It applies an aggregation function to as many input rows as possible so that writing to disk (known as a “spill”) is not necessary. Hash Match is the only physical operator (iterator) that implements partition aggregation. Partial Aggregate is a logical operator.
None	Branch Repartition	In a parallel query plan, sometimes there are conceptual regions of iterators. All of the iterators within such a region can be executed by parallel threads. The regions themselves must be executed serially. Some of the Parallelism iterators within an individual region are called Branch Repartition. The Parallelism iterator at the boundary of two such regions is called Segment Repartition. Branch Repartition and Segment Repartition are logical operators.
None	Segment Repartition	In a parallel query plan, sometimes there are conceptual regions of iterators. All of the iterators within such a region can be executed by parallel threads. The regions themselves must be executed serially. Some of the Parallelism iterators within an individual region are called Branch Repartition. The Parallelism iterator at the boundary of two such regions is called Segment Repartition. Branch Repartition and Segment Repartition are logical operators.
Arithmetic/variables
	Arithmetic Expression	The Arithmetic Expression operator computes a new value from existing values in a row. Arithmetic Expression is not used in SQL Server 2019 (15.x).
	Assign	The Assign operator assigns the value of an expression or a constant to a variable. Assign is a language element.
	Declare	The Declare operator allocates a local variable in the query plan. Declare is a language element.
	UDX	Extended Operators (UDX) implement one of many XQuery and XPath operations in SQL Server. All UDX operators are both logical and physical operators. Extended operator (UDX) FOR XML is used to serialize the relational row set it inputs into XML representation in a single BLOB column in a single output row. It is an order-sensitive XML aggregation operator. Extended operator (UDX) XML SERIALIZER is an order sensitive XML aggregation operator. It inputs rows representing XML nodes or XQuery scalars in XML document order and produces a serialized XML BLOB in a single XML column in a single output row. Extended operator (UDX) XML FRAGMENT SERIALIZER is a special type of XML SERIALIZER that is used for processing input rows representing XML fragments being inserted in XQuery insert data modification extension. Extended operator (UDX) XQUERY STRING evaluates the XQuery string value of input rows representing XML nodes. It is an order-sensitive string aggregation operator. It outputs one row with columns representing the XQuery scalar that contains the string value of the input. Extended operator (UDX) XQUERY LIST DECOMPOSER is an XQuery list decomposition operator. For each input row representing an XML node, it produces one or more rows, each representing an XQuery scalar containing a list element value if the input is of XSD list type. Extended operator (UDX) XQUERY DATA evaluates the XQuery fn:data() function on input representing XML nodes. It is an order-sensitive string aggregation operator. It outputs one row with columns representing XQuery scalar that contains the result of fn:data(). Extended operator XQUERY CONTAINS evaluates the XQuery fn:contains() function on input representing XML nodes. It is an order-sensitive string aggregation operator. It outputs one row with columns representing XQuery scalar that contains the result of fn:contains(). Extended operator UPDATE XML NODE updates XML node in the XQuery replace data modification extension in the modify() method on XML type.