From the age of 11 on, Sarah Manguso had kept a meticulous, desperate record of her life, a diary that is now over 800,000 words long. The diary was my defense against waking up at the end of my life and realizing I’d missed it. Part of the question is whether record-keeping, as an artificial form of remembrance, actually eclipses the experience it purports to capture, rather as a photograph might. In a daily journal, memory becomes fossilized without gaining meaning — revisiting her diary, Manguso writes in an afterword, she realized that it “possessed no form separate from the greater form … just day after day after day after day.” “Ongoingness,” while its brevity and controlled structure may be a kind of reaction to the amoebic collection of words of which Manguso’s diary consists — not one of which, as it happens, is quoted here — is also, in its way, a series of moments itself, though it does not seek, as the diary did, to recapture or preserve. Written in short paragraphs that hover in sets of one or two at the top of each page, “Ongoingness” is poem-like in its minimalism, the vast white space asking that the words be savored, lingered on. The afterword, in which Manguso explains her decision not to excerpt the diary, feels flat and unnecessary in comparison with the structured elegance of the rest, as though Manguso were doubting herself, failing to trust her choices as a writer. In the central and best portion of the book, though, in which Manguso examines how giving birth to her son reorganized her relationship to self and time, the writing becomes, in its fragmented, dreamlike recitation of facts and half thoughts, almost a map of the experiential world of a new mother.