This patch implements a circular buffer in tuplestore which drops old tuples as they're no longer needed. It uses this for merge joins to avoid having to spill the tuplestore if no single value exceeds work_mem. It also is what's needed for both recursive query support and OLAP window functions (hence why it implements the more complex circular buffer rather than just moving the single tuple up to the head of the buffer).
This was mostly already done by Simon, I just finished the logic in tuplesort.c. This is actually not quite polished so I guess it's still a WIP but it's certainly ready to be reviewed. All that remains is polishing. If there's anything in there people object to now I would like to know.
mergejoin-circbuffer-v1.patch.gz
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-- Gregory Stark EnterpriseDB http://www.enterprisedb.com
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