On Fri, Sep 25, 2015 at 6:49 AM, Kouhei Kaigai <kai...@ak.jp.nec.com> wrote:
> Hi, > > I tried to define two additional callbacks to support CustomScan > on readfuncs.c. > > First of all, we need to pay attention how to treat output of > TextOutCustomScan when additional text output is generated. > Only custom-scan provider knows what shall be displayed, so > all we can do is invoke a new callback: TextReadCustomScan(). > Because private fields shall be displayed next to the common > field of CustomScan, this callback is invoked once pg_strtok > pointer reached to the last field of CustomScan. Then, custom > scan provider allocates CustomScan or a structure embedding > CustomScan; only CSP knows exact size to be allocated. > It can fetch some tokens using pg_strtok and reconstruct its > private fields, but no need to restore the common field because > it shall be done by _readCustomScan. > So will the specification of TextReadCustomScan() and TextOutCustomScan() ensures that they don't access the common fields (like custom_private or others) of CustomScan? If they change/overwrite them in some way, then I think _readCustomScan() won't work because it doesn't take into account that common fields could have been updated by TextReadCustomScan(). With Regards, Amit Kapila. EnterpriseDB: http://www.enterprisedb.com
