Re: [Postgres-xc-developers] GTM Standby Crash

[Koichi S. <koi...@gm...>]

Yes, memory context usage of this part is not correct and it leaves
garbage.  I will commit it if no further input is given.

Regards;
----------
Koichi Suzuki


2013/3/7 Nikhil Sontakke <ni...@st...>:
> Hi,
>
> PFA, patch which fixes an obnoxious crash in GTM Standby. This one was
> a tough nut to crack down. The crash is as below
>
> Program terminated with signal 11, Segmentation fault.
> #0  0x00000000004253c9 in gtm_lappend ()
> Missing separate debuginfos, use: debuginfo-install
> glibc-2.12-1.80.el6_3.6.x86_64 libgcc-4.4.6-4.el6.x86_64
> (gdb) bt
> #0  0x00000000004253c9 in gtm_lappend ()
> #1  0x000000000040ad77 in GTM_BkupBeginTransactionGetGXIDMulti.clone.0 ()
> #2  0x000000000040aedb in ProcessBkupBeginTransactionGetGXIDCommand ()
> #3  0x000000000040417c in GTM_ThreadMain ()
>
>
>
> IMHO, using TopMemoryContext to mean the top context of each thread is
> pretty confusing. Bad choice of name for the memory context according
> to me. Maybe we could have avoided this crash if we had used a
> different name for the context.
>
> This "TopMemoryContext" goes away when that thread goes away. So ain't
> nothing TOP about it. The GTMTransactions.gt_open_transactions list
> was being appended to using this memory context. So later if another
> thread came in (and the earlier appending thread had been cleaned up),
> it will find garbage in this list and this was causing the crash.
>
> I always saw a couple of threads being cleaned up in the gtm standby
> logs just prior to the crash. The fix is to use TopMostMemoryContext.
> If it were to me I would re-haul this TopMemoryContext naming business
> in GTM. Am sure people will get confused in the future too when they
> write code..
>
> Regards,
> Nikhils
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