database/postgres
database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-04-22 23:02:54 +03:00
Code

Improve comment in hashsearch.c.

Browse Source 
Typo fix from Mithun Cy; other improvements by me.
This commit is contained in:
Robert Haas 2017-01-18 16:36:48 -05:00
parent 1586317c3f
commit e37360d5df
1 changed files with 11 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

21
src/backend/access/hash/hashsearch.c
View File

@ -334,19 +334,20 @@ _hash_first(IndexScanDesc scan, ScanDirection dir)
so->hashso_bucket_buf = buf;
/*
* If the bucket split is in progress, then while scanning the bucket
* being populated, we need to skip tuples that are moved from bucket
* being split. We need to maintain the pin on bucket being split to
* If a bucket split is in progress, then while scanning the bucket being
* populated, we need to skip tuples that were copied from bucket being
* split. We also need to maintain a pin on the bucket being split to
* ensure that split-cleanup work done by vacuum doesn't remove tuples
* from it till this scan is done. We need to main to maintain the pin on
* from it till this scan is done. We need to maintain a pin on the
* bucket being populated to ensure that vacuum doesn't squeeze that
* bucket till this scan is complete, otherwise the ordering of tuples
* bucket till this scan is complete; otherwise, the ordering of tuples
* can't be maintained during forward and backward scans. Here, we have
* to be cautious about locking order, first acquire the lock on bucket
* being split, release the lock on it, but not pin, then acquire the lock
* on bucket being populated and again re-verify whether the bucket split
* still is in progress. First acquiring lock on bucket being split
* ensures that the vacuum waits for this scan to finish.
* to be cautious about locking order: first, acquire the lock on bucket
* being split; then, release the lock on it but not the pin; then,
* acquire a lock on bucket being populated and again re-verify whether
* the bucket split is still in progress. Acquiring the lock on bucket
* being split first ensures that the vacuum waits for this scan to
* finish.
*/
if (H_BUCKET_BEING_POPULATED(opaque))
{