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Previously, we had consecutive, very short chapters called "Generic WAL" and "Custom WAL Resource Managers," explaining different approaches to the same problem. Merge them into a single chapter. Explain most of the differences between the approaches in the chapter's introductory text, rather than in the individual sections. Discussion: http://postgr.es/m/46ac50c1-6b2a-404f-a683-b67af6ab56e9@eisentraut.org