Does PHP's pg_fetch_assoc() use an Iterator/Cursor?

Question

Does the PHP function pg_fetch_assoc() internally

use an Iterator / Cursor, or does it get all data at once, network-wise?

Would \PDO be using a Cursor?

My context is fetching a large amount of data and I want to know if it gets pulled as a whole or row by row (or limited rows by rows when the cursor holds a subset of the full dataset).

Answer 1

The data is passed via $result:

(Taken from the pgsql.php file that opens (CTRL + Click on function name in PHPStorm)):

/**
 * Fetch a row as an associative array
 * @link https://php.net/manual/en/function.pg-fetch-assoc.php
 * @param resource $result <p>
 * PostgreSQL query result resource, returned by <b>pg_query</b>,
 * <b>pg_query_params</b> or <b>pg_execute</b>
 * (among others).
 * </p>
 * @param int $row [optional] <p>
 * Row number in result to fetch. Rows are numbered from 0 upwards. If
 * omitted or <b>NULL</b>, the next row is fetched.
 * </p>
 * @return array An array indexed associatively (by field name).
 * Each value in the array is represented as a
 * string. Database NULL
 * values are returned as <b>NULL</b>.
 * </p>
 * <p>
 * <b>FALSE</b> is returned if <i>row</i> exceeds the number
 * of rows in the set, there are no more rows, or on any other error.
 * @since 4.3
 * @since 5.0
 */
function pg_fetch_assoc ($result, $row = null) {}

The rows in $result is a numbered array/object, containing all data it has. It simply returns the row in that array/object, so it deals with whatever data is in the passed cursor. We can get this from one of the lines from the above code (formatted for better reading):

@param resource $result
PostgreSQL query result resource, returned by
pg_query, pg_query_params or pg_execute

Answer 2

pg_fetch_assoc() does neither. It is a function which fetches an associative array from a PHP resource. The resource can be for example the result of the call to PQexecPrepared.

On API level PHP-pgsql does not have cursor functions. You could try using PDO, which emulates cursors for PostgreSQL if you enable the scrollable cursor mode. See prepare() for more details. Another alternative is to just use the SQL cursor statements yourself.

This answer explains a little bit more: php postgres from query to fetching rows in theory

Here is a link to PDO source code, which is responsible for emulating cursors with SQL statements.