I've been wondering what the behavior of postgres is when the server process stops, for whatever reason, at certain critical points in the execution flow.
In the following example the client will only regard the data as stored until
the COMMIT command is successfully executed. But the the server, client or
network may fail at any point during the execution and therefore the server and
client may not be in sync of what the current state is.
BEGIN;
INSERT INTO ....;
COMMIT;
To experiment with this I inserted a stupid if statement (see patch) which will
make the server process exit(1) if the client sends a COMMIT command, but only
after the COMMIT command has been processed on the server and just before the
server send the close commend (wire protocol). I.e. the server has COMMITed the
transaction, but the client just experiences that the connection has been
closed for some reason:
server closed the connection unexpectedly
This probably means the server terminated abnormally
before or while processing the request.
The connection to the server was lost. Attempting reset: Succeeded.
So my question is, how should the client handle these situations? I think most
systems will have some variation of the following:
try
execute transactional sql
catch (commit failed)
// regard data as not stored
But, this doesn't seem to be enough, so I guess you would have to do something
like:
try
execute transactional sql
catch (commit failed)
if (data is not stored)
// regard data as not stored
Thanks in advance.
/Håvar Nøvik
0001-exit-before-close-on-commit-command.patch
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