On 26 January 2017 at 21:42, Tom Lane <t...@sss.pgh.pa.us> wrote: > Craig Ringer <craig.rin...@2ndquadrant.com> writes: >> One suggestion: it's currently non-obvious that ProcessUtility_hook >> gets called with the full text of all parts of a multi-statement. > > OK, we can improve that ... > >> The same query string may be passed to multiple invocations of >> ProcessUtility >> if a utility statement in turn invokes other utility statements, or if the >> user supplied a query string containing multiple semicolon-separated >> statements in a single protocol message. It is also possible for the query >> text to contain other non-utility-statement text like comments, empty >> statements, and plannable statements. Callers that use the queryString >> should use pstmt->stmt_location and pstmt->stmt_len to extract the text for >> the statement of interest and should guard against re-entrant invocation. > > Not sure about the reference to re-entrancy. It's not especially relevant > to query texts AFAICS, and wouldn't a utility statement know darn well if > it was doing something that could end up invoking another instance of > itself?
The utility statement does, but the hooks don't necessarily. If you fire an ALTER TABLE ... ADD COLUMN .. ADD COLUMN .. ADD CONSTRAINT ..; for example. However, I was wrong to say we must guard against re-entrancy. We should only enter ProcessUtility once with context == PROCESS_UTILITY_QUERY, and that's what hooks should be looking at rather than keeping track of re-entrant invocations. So perhaps: "The same query string may be passed to multiple invocations of ProcessUtility if a utility statement invokes subcommands (e.g. ALTER TABLE), in which case context will be set to PROCESS_UTILITY_SUBCOMMAND, or if the user supplied a query string containing multiple semicolon-separated statements in a single protocol message. It is also possible for the query text to contain other non-utility-statement text like comments, empty statements, and plannable statements that don't pass through ProcessUtility. Hooks that use the queryString should use pstmt->stmt_location and pstmt->stmt_len to extract the text for the statement of interest and should pay attention to the context to avoid repeatedly handling the same query string in subcommands." -- Craig Ringer http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
