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Minor safekeeper readme fix.

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Arseny Sher
2021-10-11 16:31:44 +03:00
parent d7c9dd06f4
commit 8c61c3e54e
1 changed files with 6 additions and 6 deletions
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walkeeper/README
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@@ -89,12 +89,12 @@ A: Page Server is a single server which can be lost. As our primary
Q: What if the compute node evicts a page, needs it back, but the page is yet
to reach the Page Server?
A: If the compute node has evicted a page, all changes from that page are
already committed, i.e. they are saved on majority of WAL safekeepers. These
WAL records will eventually reach the Page Server. The Page Server notes
that the compute note requests pages with a very recent LSN and will not
respond to the compute node until it a corresponding WAL is received from WAL
safekeepers.
A: If the compute node has evicted a page, changes to it have been WAL-logged
(that's why it is called Write Ahead logging; there are some exceptions like
index builds, but these are exceptions). These WAL records will eventually
reach the Page Server. The Page Server notes that the compute note requests
pages with a very recent LSN and will not respond to the compute node until a
corresponding WAL is received from WAL safekeepers.
Q: How long may Page Server wait for?
A: Not too long, hopefully. If a page is evicted, it probably was not used for