Update.php

<?php

namespace Drupal\Core\Database\Driver\pgsql;

use Drupal\Core\Database\Database;
use Drupal\Core\Database\Query\Update as QueryUpdate;
use Drupal\Core\Database\Query\SelectInterface;

/**
 * PostgreSQL implementation of \Drupal\Core\Database\Query\Update.
 */
class Update extends QueryUpdate {
    public function execute() {
        $max_placeholder = 0;
        $blobs = [];
        $blob_count = 0;
        // Because we filter $fields the same way here and in __toString(), the
        // placeholders will all match up properly.
        $stmt = $this->connection
            ->prepareQuery((string) $this);
        // Fetch the list of blobs and sequences used on that table.
        $table_information = $this->connection
            ->schema()
            ->queryTableInformation($this->table);
        // Expressions take priority over literal fields, so we process those first
        // and remove any literal fields that conflict.
        $fields = $this->fields;
        foreach ($this->expressionFields as $field => $data) {
            if (!empty($data['arguments'])) {
                foreach ($data['arguments'] as $placeholder => $argument) {
                    // We assume that an expression will never happen on a BLOB field,
                    // which is a fairly safe assumption to make since in most cases
                    // it would be an invalid query anyway.
                    $stmt->bindParam($placeholder, $data['arguments'][$placeholder]);
                }
            }
            if ($data['expression'] instanceof SelectInterface) {
                $data['expression']->compile($this->connection, $this);
                $select_query_arguments = $data['expression']->arguments();
                foreach ($select_query_arguments as $placeholder => $argument) {
                    $stmt->bindParam($placeholder, $select_query_arguments[$placeholder]);
                }
            }
            unset($fields[$field]);
        }
        foreach ($fields as $field => $value) {
            $placeholder = ':db_update_placeholder_' . $max_placeholder++;
            if (isset($table_information->blob_fields[$field])) {
                $blobs[$blob_count] = fopen('php://memory', 'a');
                fwrite($blobs[$blob_count], $value);
                rewind($blobs[$blob_count]);
                $stmt->bindParam($placeholder, $blobs[$blob_count], \PDO::PARAM_LOB);
                ++$blob_count;
            }
            else {
                $stmt->bindParam($placeholder, $fields[$field]);
            }
        }
        if (count($this->condition)) {
            $this->condition
                ->compile($this->connection, $this);
            $arguments = $this->condition
                ->arguments();
            foreach ($arguments as $placeholder => $value) {
                $stmt->bindParam($placeholder, $arguments[$placeholder]);
            }
        }
        $options = $this->queryOptions;
        $options['already_prepared'] = TRUE;
        $options['return'] = Database::RETURN_AFFECTED;
        $this->connection
            ->addSavepoint();
        try {
            $result = $this->connection
                ->query($stmt, [], $options);
            $this->connection
                ->releaseSavepoint();
            return $result;
        } catch (\Exception $e) {
            $this->connection
                ->rollbackSavepoint();
            throw $e;
        }
    }

}