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Backpatch-through: 13
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Presently, each iteration of the loop in sift_down() will perform
3 comparisons if both children are larger than the parent node (2
for comparing each child to the parent node, and a third to compare
the children to each other). By first comparing the children to
each other and then comparing the larger child to the parent node,
we can accomplish the same thing with just 2 comparisons (while
also not affecting the number of comparisons in any other case).
Author: ChangAo Chen
Reviewed-by: Robert Haas
Discussion: https://postgr.es/m/tencent_0142D8DA90940B9930BCC08348BBD6D0BB07%40qq.com
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This reverts commit b840508644 and bcb14f4abc. These commits were made
for commit 5bec1d6bc5 (Improve eviction algorithm in ReorderBuffer
using max-heap for many subtransactions). However, per discussion,
commit efb8acc0d0 replaced binary heap + index with pairing heap, and
made these commits unnecessary.
Reported-by: Jeff Davis
Discussion: https://postgr.es/m/12747c15811d94efcc5cda72d6b35c80d7bf3443.camel%40j-davis.com
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Previously, binaryheap didn't support updating a key and removing a
node in an efficient way. For example, in order to remove a node from
the binaryheap, the caller had to pass the node's position within the
array that the binaryheap internally has. Removing a node from the
binaryheap is done in O(log n) but searching for the key's position is
done in O(n).
This commit adds a hash table to binaryheap in order to track the
position of each nodes in the binaryheap. That way, by using newly
added functions such as binaryheap_update_up() etc., both updating a
key and removing a node can be done in O(1) on an average and O(log n)
in worst case. This is known as the indexed binary heap. The caller
can specify to use the indexed binaryheap by passing indexed = true.
The current code does not use the new indexing logic, but it will be
used by an upcoming patch.
Reviewed-by: Vignesh C, Peter Smith, Hayato Kuroda, Ajin Cherian,
Tomas Vondra, Shubham Khanna
Discussion: https://postgr.es/m/CAD21AoDffo37RC-eUuyHJKVEr017V2YYDLyn1xF_00ofptWbkg%40mail.gmail.com
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The node array space of the binaryheap is doubled when there is no
available space.
Reviewed-by: Vignesh C, Peter Smith, Hayato Kuroda, Ajin Cherian,
Tomas Vondra, Shubham Khanna
Discussion: https://postgr.es/m/CAD21AoDffo37RC-eUuyHJKVEr017V2YYDLyn1xF_00ofptWbkg%40mail.gmail.com
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Reported-by: Michael Paquier
Discussion: https://postgr.es/m/ZZKTDPxBBMt3C0J9@paquier.xyz
Backpatch-through: 12
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This commit introduces binaryheap_remove_node(), which can be used
to remove any node from a binary heap. The implementation is
straightforward. The target node is replaced with the last node in
the heap, and then we sift as needed to preserve the heap property.
This new function is intended for use in a follow-up commit that
will improve the performance of pg_restore.
Reviewed-by: Tom Lane
Discussion: https://postgr.es/m/3612876.1689443232%40sss.pgh.pa.us
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There are a couple of places in frontend code that could make use
of this simple binary heap implementation. This commit makes
binaryheap usable in frontend code, much like commit 26aaf97b68 did
for StringInfo. Like StringInfo, the header file is left in lib/
to reduce the likelihood of unnecessary breakage.
The frontend version of binaryheap exposes a void *-based API since
frontend code does not have access to the Datum definitions. This
seemed like a better approach than switching all existing uses to
void * or making the Datum definitions available to frontend code.
Reviewed-by: Tom Lane, Alvaro Herrera
Discussion: https://postgr.es/m/3612876.1689443232%40sss.pgh.pa.us
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