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There's long been a "TODO: there might be some value in caching the results" annotation on pg_dump's getFormattedTypeName function; but we hadn't gotten around to checking what it was costing us to repetitively look up type names. It turns out that when dumping the current regression database, about 10% of the total number of queries issued are duplicative format_type() queries. However, Hubert Depesz Lubaczewski reported a not-unusual case where these account for over half of the queries issued by pg_dump. Individually these queries aren't expensive, but when network lag is a factor, they add up to a problem. We can very easily add some caching to getFormattedTypeName to solve it. Since this is such a simple fix and can have a visible performance benefit, back-patch to all supported branches. Discussion: https://postgr.es/m/20210826084430.GA26282@depesz.com
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