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Prefetching has been implemented

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Heikki Linnakangas
2024-06-18 13:30:58 +03:00
committed by Heikki Linnakangas
parent 0396ed67f7
commit 33a09946fc
1 changed files with 12 additions and 13 deletions
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docs/core_changes.md
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@@ -21,6 +21,18 @@ compute, and changes needed for the WAL redo process:
# Changes for Compute node
## Prefetching
There are changes in many places to perform prefetching, for example for sequential scans. Neon
doesn't benefit from OS readahead, and the latency to pageservers is quite high compared to local
disk, so prefetching is critical for performance, also for sequential scans.
### How to get rid of the patch
Upcoming "streaming read" work in v17 might simplify this. And async I/O work in v18 will hopefully
do more.
## Add t_cid to heap WAL records
```
@@ -482,19 +494,6 @@ hint bits are set. Wal logging hint bits updates requires FPI which significantl
Add special WAL record for setting page hints.
## Prefetching
### Why?
As far as pages in Neon are loaded on demand, to reduce node startup time
and also speedup some massive queries we need some mechanism for bulk loading to
reduce page request round-trip overhead.
Currently Postgres is supporting prefetching only for bitmap scan.
In Neon we should also use prefetch for sequential and index scans, because the OS is not doing it for us.
For sequential scan we could prefetch some number of following pages. For index scan we could prefetch pages
of heap relation addressed by TIDs.
## Prewarming
### Why?