Hi Hackers,
The SnapBuildPurgeOlderTxn function previously used a suboptimal
method to remove old XIDs from the committed.xip array. It allocated a
temporary workspace array, copied the surviving elements into it, and
then copied them back, incurring unnecessary memory allocation and
multiple data copies.
This patch refactors the logic to use a standard two-pointer, in-place
compaction algorithm. The new approach filters the array in a single
pass with no extra memory allocation, improving both CPU and memory
efficiency.
No behavioral changes are expected. This resolves a TODO comment
expecting a more efficient algorithm.
Best,
Xuneng
