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Michael Paquier 70b4f82a4b Prevent hard failures of standbys caused by recycled WAL segments ... When a standby's WAL receiver stops reading WAL from a WAL stream, it writes data to the current WAL segment without having priorily zero'ed the page currently written to, which can cause the WAL reader to read junk data from a past recycled segment and then it would try to get a record from it. While sanity checks in place provide most of the protection needed, in some rare circumstances, with chances increasing when a record header crosses a page boundary, then the startup process could fail violently on an allocation failure, as follows: FATAL: invalid memory alloc request size XXX This is confusing for the user and also unhelpful as this requires in the worst case a manual restart of the instance, impacting potentially the availability of the cluster, and this also makes WAL data look like it is in a corrupted state. The chances of seeing failures are higher if the connection between the standby and its root node is unstable, causing WAL pages to be written in the middle. A couple of approaches have been discussed, like zero-ing new WAL pages within the WAL receiver itself but this has the disadvantage of impacting performance of any existing instances as this breaks the sequential writes done by the WAL receiver. This commit deals with the problem with a more simple approach, which has no performance impact without reducing the detection of the problem: if a record is found with a length higher than 1GB for backends, then do not try any allocation and report a soft failure which will force the standby to retry reading WAL. It could be possible that the allocation call passes and that an unnecessary amount of memory is allocated, however follow-up checks on records would just fail, making this allocation short-lived anyway. This patch owes a great deal to Tsunakawa Takayuki for reporting the failure first, and then discussing a couple of potential approaches to the problem. Backpatch down to 9.5, which is where palloc_extended has been introduced. Reported-by: Tsunakawa Takayuki Reviewed-by: Tsunakawa Takayuki Author: Michael Paquier Discussion: https://postgr.es/m/0A3221C70F24FB45833433255569204D1F8B57AD@G01JPEXMBYT05		8 years ago
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backend	Prevent hard failures of standbys caused by recycled WAL segments	8 years ago
bin	Use snprintf not sprintf in pg_waldump's timestamptz_to_str.	8 years ago
common	Adjust error message	8 years ago
fe_utils	Post-feature-freeze pgindent run.	8 years ago
include	Remove AELs from subxids correctly on standby	8 years ago
interfaces	Avoid unnecessary use of strncpy in a couple of places in ecpg.	8 years ago
makefiles	Remove Windows module-list-dumping code.	8 years ago
pl	Don't fall off the end of perl functions	8 years ago
port	Fix simple_prompt() to disable echo on Windows when stdin != terminal.	8 years ago
template	…
test	Fix some minor error-checking oversights in ParseFuncOrColumn().	8 years ago
timezone	Update time zone data files to tzdata release 2018e.	8 years ago
tools	Exclude files in .git from list of perl files	8 years ago
tutorial	…
.gitignore	…
DEVELOPERS	…
Makefile	…
Makefile.global.in	Un-break contrib install with llvm.	8 years ago
Makefile.shlib	…
nls-global.mk	…