PLV8 Built-ins

PLV8 includes a number of built-in functions bound to the plv8 object for you to use.

Utility Functions


plv8.elog emits a message to the client or the PostgreSQL log file. The emit level is one of:

  • DEBUG5
  • DEBUG4
  • DEBUG3
  • DEBUG2
  • DEBUG1
  • LOG
  • INFO

``` var msg = 'world';

plv8.elog(DEBUG1, 'Hello', ${msg}!); ```

See the PostgreSQL manual for information on each error level.

plv8.quote_literal, plv8.nullable, plv8.quote_ident

Each function for the quote family is identical to the built-in SQL function with the same name.


PLV8 provides a function to access other functions defined as plv8 functions that have been registered in the database.

CREATE FUNCTION callee(a int) RETURNS int AS $$ return a * a $$ LANGUAGE plv8; CREATE FUNCTION caller(a int, t int) RETURNS int AS $$ var func = plv8.find_function("callee"); return func(a); $$ LANGUAGE plv8;

With plv8.find_function()``, you can look up other PLV8 functions. If they are not a PLV8 function, and error is thrown. The function signature parameter toplv8.find_function()` is either ofregproc(function name only) or regprocedure` (function name with argument types). You can make use of the internal type for arguments and void type for return type for the pure Javascript function to make sure any invocation from SQL statements should not occur.


The plv8 object provides a version string as plv8.version. This string corresponds to the plv8 module version.


You can get your own memory usage by calling plv8.memory_usage() with no params. The resulting object looks like this: json { "total_heap_size":1327104, "total_physical_size":472712, "used_heap_size":381748, "heap_size_limit":270008320, "external_memory":0, "number_of_native_contexts":2 }

See nodejs v8.getHeapStatistics()


Run a script from source code, it's like eval() but takes a second argument: script name
Can be pretty useful for debugging

Can be used like this js const sourceCode = `globalThis.myFunc = () => 42` try { plv8.run_script(sourceCode, 'myScript.js') myFunc() } catch (e) { plv8.elog(NOTICE, e.message) }

Database Access via SPI

PLV8 provides functions for database access, including prepared statements, and cursors.


plv8.execute(sql [, args])

Executes SQL statements and retrieves the results. The sql argument is required, and the args argument is an optional array containing any arguments passed in the SQL query. For SELECT queries, the returned value is an array of objects. Each object represents one row, with the object properties mapped as column names. For non-SELECT queries, the return result is the number of rows affected.

var json_result = plv8.execute('SELECT * FROM tbl'); var num_affected = plv8.execute('DELETE FROM tbl WHERE price > $1', [ 1000 ]);


plv8.prepare(sql [, typenames])

Opens or creates a prepared statement. The typename parameter is an array where each element is a string that corresponds to the PostgreSQL type name for each bind parameter. Returned value is an object of the PreparedPlan type. This object must be freed by before leaving the function.

``` var plan = plv8.prepare('SELECT * FROM tbl WHERE col = $1', [ 'int' ]); var rows = plan.execute([ 1 ]); var sum = 0; for (var i = 0; i < rows.length; i++) { sum += rows[i].num; };

return sum; ```


PreparedPlan.execute([ args ])

Executes the prepared statement. The args parameter is the same as what would be required for plv8.execute(), and can be omitted if the statement does not have any parameters. The result of this method is also the same as plv8.execute().


PreparedPlan.cursor([ args ])

Opens a cursor form the prepared statement. The args parameter is the same as what would be required for plv8.execute() and PreparedPlan.execute(). The returned object is of type Cursor. This must be closed by Cursor.close() before leaving the function.

``` var plan = plv8.prepare('SELECT * FROM tbl WHERE col = $1', [ 'int' ]); var cursor = plan.cursor([ 1 ]); var sum = 0, row; while (row = cursor.fetch()) { sum += row.num; } cursor.close();;

return sum; ```

Frees the prepared statement.


Cursor.fetch([ nrows ])

When the nrows parameter is omitted, fetches a row from the cursor and returns it as an object (note: not as an array). If specified, fetches as many rows as the nrows parameter, up to the number of rows available, and returns an array of objects. A negative value will fetch backward.



Moves the cursor nrows. A negative value will move backward.


Closes the Cursor.



plv8.execute() creates a subtransaction each time it executes. If you need an atomic operation, you will need to call plv8.subtransaction() to create a subtransaction block.

try{ plv8.subtransaction(function(){ plv8.execute("INSERT INTO tbl VALUES(1)"); // should be rolled back! plv8.execute("INSERT INTO tbl VALUES(1/0)"); // occurs an exception }); } catch(e) { ... execute fall back plan ... }

If one of the SQL execution in the subtransaction block fails, all of operations within the block are rolled back. If the process in the block throws a Javascript exception, it is carried forward. So use a try ... catch block to capture it and do alternative operations if it occurs.

Window Function API

You can define user-defined window functions with PLV8. It wraps the C-level window function API to support full functionality. To create one, first obtain a window object by calling plv8.get_window_object(), which provides the following interfaces:


Returns the current position in the partition, starting from 0.


Returns the number of rows in the partition.



Sets the mark at the specified row. Rows above this position will be gone and no longer accessible later.


WindowObject.rows_are_peers(pos1, pos1)

Returns true if the rows at pos1 and pos2 are peers.


WindowObject.get_func_arg_in_partition(argno, relpos, seektype, mark_pos)


WindowObject.get_func_arg_in_frame(argno, relpos, seektype, mark_pos)

Returns the value of the argument in argno (starting from 0) to this function at the relpos row from seektype in the current partition or frame. seektype can be either of WindowObject.SEEK_HEAD, WindowObject.SEEK_CURRENT, or WindowObject.SEEK_TAIL. If mark_pos is true, the row the argument is fetched from is marked. If the specified row is out of the partition/frame, the returned value will be undefined.



Returns the value of the argument in argno (starting from 0) to this function at the current row. Note that the returned value will be the same as the argument variable of the function.


WindowObject.get_partition_local([ size ])

Returns partition-local value, which is released at the end of the current partition. If nothing is stored, undefined is returned. size argument (default 1000) is the byte size of the allocated memory in the first call. Once the memory is allocated, the size will not change.



Stores the partition-local value, which you can retrieve later with get_partition_local(). This function internally uses JSON.stringify() to serialize the object, so if you pass a value that is not able to be serialized it may end up being an unexpected value. If the size of a serialized value is more than the allocated memory, it will throw an exception.

You can also learn more on how to use these API in the sql/window.sql regression test, which implements most of the native window functions. For general information on the user-defined window function, see the CREATE FUNCTION page of the PostgreSQL manual.