supported versions of our database system, including 11.2, 10.7, 9.6.12,
9.5.16, and 9.4.21. This release changes the behavior in how PostgreSQL
interfaces with `fsync()` and includes fixes for partitioning and over
70 other bugs that were reported over the past three months.
Users should plan to apply this update at the next scheduled downtime.
FreeBSD port adds OPTIONS knob to support LLVM JIT. [1]
Highlight: Change in behavior with fsync()
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When available in an operating system and enabled in the configuration
file (which it is by default), PostgreSQL uses the kernel function
`fsync()` to help ensure that data is written to a disk. In some
operating systems that provide `fsync()`, when the kernel is unable to
write out the data, it returns a failure and flushes the data that was
supposed to be written from its data buffers.
This flushing operation has an unfortunate side-effect for PostgreSQL:
if PostgreSQL tries again to write the data to disk by again calling
`fsync()`, `fsync()` will report back that it succeeded, but the data
that PostgreSQL believed to be saved to the disk would not actually be
written. This presents a possible data corruption scenario.
This update modifies how PostgreSQL handles a `fsync()` failure:
PostgreSQL will no longer retry calling `fsync()` but instead will
panic. In this case, PostgreSQL can then replay the data from the
write-ahead log (WAL) to help ensure the data is written. While this may
appear to be a suboptimal solution, there are presently few alternatives
and, based on reports, the problem case occurs extremely rarely.
A new server parameter `data_sync_retry` has been added to manage this
behavior. If you are certain that your kernel does not discard dirty
data buffers in such scenarios, you can set `data_sync_retry` to `on` to
restore the old behavior.
Release Notes: https://www.postgresql.org/about/news/1920/
PR: 232490 [1]
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