On 2 August 2018 at 21:32, Peter Geoghegan <p...@bowt.ie> wrote: If I want to sort on heap TID as a tie-breaker, I cannot cut any > corners. That is, it has to be just another column, at least as far as > the implementation is concerned (heap TID will have a different > representation in internal pages and leaf high keys, but nonetheless > it's essentially just another column in the keyspace). This means that > if I don't have suffix truncation, I'll regress performance in many > important cases that have no compensating benefit (e.g. pgbench). > There is no point in trying to assess that. >
If you include heap TID as a column the suffix will be unique and cannot benefit from suffix truncation. It would be better to avoid including the heap TID as a column, since it is already there. Or the other way around, don't include it as payload if it is has to be a column. Alternatively, include only the heap block number. That would make it non-unique, but never more than 240 duplicates. So it would allow suffix truncation, and yet still avoid the multi-page split effect. -- Simon Riggs http://www.2ndQuadrant.com/ <http://www.2ndquadrant.com/> PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
