I have a PostGIS table with linestring geometries and point (A) on it and I need to detrimine points (M) which located M meters from A. Distance is measured along linestrings. Any thoughts?
You could use pgRouting driving_distance(). If your point A is a node in the network, it's easy. Otherwise you'll probably have to introduce a temporary node.
An example using pgRouting 100 km around a node: