Обсуждение: How to find calculated CRC checksum of pg_controldata
Hello, Question: Is there a way to obtain the calculated CRC checksum for pg_controldata from the command line? I'm asking this because we had our database get wiped out, and for a variety of reasons, did not have a clean backup of the data directory. I did, however, have a complete set of WAL files for the database from the origin of the instance's life. I was able to use these to restore the database into a new database that I engineered look like a copy of the original by editing the pg_control file (and first log file) by changing the Database system identifier and the CRC checksum. Finding the correct CRC checksum, however, was a pain. I downloaded the code and modified pg_controldata.exe so it would display the file CRC and calculated checksums so I would know what the correct value was. I'm in the process of documenting what I did and it would make the whole process much easier if there is a way to determine the CRC checksum without having to dig into the source code. I am currently using 9.2.6. Thanks for any info, Matt, who was extremely lucky that I initiated WAL logging at the very beginning. -- Matthew J Rantala, GISP Minnesota Geological Survey University of Minnesota 2642 University Ave. St. Paul, MN 55114-1057 (612) 627-4780 x206
On Thu, Apr 3, 2014 at 08:58:26AM -0500, Matthew Rantala wrote: > Hello, > > Question: Is there a way to obtain the calculated CRC checksum for > pg_controldata from the command line? > > I'm asking this because we had our database get wiped out, and for a > variety of reasons, did not have a clean backup of the data > directory. I did, however, have a complete set of WAL files for the > database from the origin of the instance's life. I was able to use > these to restore the database into a new database that I engineered > look like a copy of the original by editing the pg_control file (and > first log file) by changing the Database system identifier and the > CRC checksum. > > Finding the correct CRC checksum, however, was a pain. I downloaded > the code and modified pg_controldata.exe so it would display the > file CRC and calculated checksums so I would know what the correct > value was. > > I'm in the process of documenting what I did and it would make the > whole process much easier if there is a way to determine the CRC > checksum without having to dig into the source code. I am currently > using 9.2.6. > > Thanks for any info, > > Matt, who was extremely lucky that I initiated WAL logging at the > very beginning. Did you try pg_resetxlog? That should set the checksum properly. -- Bruce Momjian <bruce@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + Everyone has their own god. +
On 4/9/2014 11:44 AM, Bruce Momjian wrote: > On Thu, Apr 3, 2014 at 08:58:26AM -0500, Matthew Rantala wrote: >> Hello, >> >> Question: Is there a way to obtain the calculated CRC checksum for >> pg_controldata from the command line? > Did you try pg_resetxlog? That should set the checksum properly. > Thanks, Bruce I think I actually tried that and while it did correct the checksum, I think it also closed/finalized the first log file (00000001000000000000001) and modified the checkpoint locations which wasn't going to work in my recovery. There may be a way to avoid that by passing the correct parameters, but I found digging into the source code easier. Thanks again, Matt -- Matthew J Rantala, GISP Minnesota Geological Survey University of Minnesota 2642 University Ave. St. Paul, MN 55114-1057 (612) 627-4780 x206