8bbe4cbd9b
If we can't read the query texts file (whether because out-of-memory, or for some other reason), give up and reset the file to empty, discarding all stored query texts, though not the statistics per se. We used to leave things alone and hope for better luck next time, but the problem is that the file is only going to get bigger and even harder to slurp into memory. Better to do something that will get us out of trouble. Likewise reset the file to empty for any other failure within gc_qtexts(). The previous behavior after a write error was to discard query texts but not do anything to truncate the file, which is just weird. Also, increase the maximum supported file size from MaxAllocSize to MaxAllocHugeSize; this makes it more likely we'll be able to do a garbage collection successfully. Also, fix recalculation of mean_query_len within entry_dealloc() to match the calculation in gc_qtexts(). The previous coding overlooked the possibility of dropped texts (query_len == -1) and would underestimate the mean of the remaining entries in such cases, thus possibly causing excess garbage collection cycles. In passing, add some errdetail to the log entry that complains about insufficient memory to read the query texts file, which after all was Jim Nasby's original complaint. Back-patch to 9.4 where the current handling of query texts was introduced. Peter Geoghegan, rather editorialized upon by me
The PostgreSQL contrib tree
---------------------------
This subtree contains porting tools, analysis utilities, and plug-in
features that are not part of the core PostgreSQL system, mainly
because they address a limited audience or are too experimental to be
part of the main source tree. This does not preclude their
usefulness.
User documentation for each module appears in the main SGML
documentation.
When building from the source distribution, these modules are not
built automatically, unless you build the "world" target. You can
also build and install them all by running "make all" and "make
install" in this directory; or to build and install just one selected
module, do the same in that module's subdirectory.
Some directories supply new user-defined functions, operators, or
types. To make use of one of these modules, after you have installed
the code you need to register the new SQL objects in the database
system by executing a CREATE EXTENSION command. In a fresh database,
you can simply do
CREATE EXTENSION module_name;
See the PostgreSQL documentation for more information about this
procedure.