| From: | Dilip Kumar <dilipbalaut(at)gmail(dot)com> |
|---|---|
| To: | "houzj(dot)fnst(at)fujitsu(dot)com" <houzj(dot)fnst(at)fujitsu(dot)com> |
| Cc: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com>, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, Greg Nancarrow <gregn4422(at)gmail(dot)com>, Euler Taveira <euler(at)eulerto(dot)com>, Peter Smith <smithpb2250(at)gmail(dot)com>, Peter Eisentraut <peter(dot)eisentraut(at)enterprisedb(dot)com>, Önder Kalacı <onderkalaci(at)gmail(dot)com>, japin <japinli(at)hotmail(dot)com>, Michael Paquier <michael(at)paquier(dot)xyz>, David Steele <david(at)pgmasters(dot)net>, Craig Ringer <craig(at)2ndquadrant(dot)com>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Amit Langote <amitlangote09(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Rahila Syed <rahilasyed90(at)gmail(dot)com> |
| Subject: | Re: row filtering for logical replication |
| Date: | 2021-07-27 04:26:33 |
| Message-ID: | CAFiTN-sE0W0WQMvz5+5D+V=cvZ-RD=nTBc8+fDvDWXB=hp9z-A@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tue, Jul 27, 2021 at 6:21 AM houzj(dot)fnst(at)fujitsu(dot)com
<houzj(dot)fnst(at)fujitsu(dot)com> wrote:
> 1) UPDATE a nonkey column in publisher.
> 2) Use debugger to block the walsender process in function
> pgoutput_row_filter_exec_expr().
> 3) Open another psql to connect the publisher, and drop the table which updated
> in 1).
> 4) Unblock the debugger in 2), and then I can see the following error:
> ---
> ERROR: could not read block 0 in file "base/13675/16391"
Yeah, that's a big problem, seems like the expression evaluation
machinery directly going and detoasting the externally stored data
using some random snapshot. Ideally, in walsender we can never
attempt to detoast the data because there is no guarantee that those
data are preserved. Somehow before going to the expression evaluation
machinery, I think we will have to deform that tuple and need to do
something for the externally stored data otherwise it will be very
difficult to control that inside the expression evaluation.
--
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com
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