Re: [HACKERS] increasing the default WAL segment size

Hello all,

Please find attached a patch to make wal segment size initdb configurable.

The attached patch removes --with-wal-segsize configure option and adds a new initdb option --wal-segsize. The module initdb passes the wal-segsize value into an environment variable which is used to overwrite the guc value wal_ segment_size and set the internal variables : XLogSegSize and XLOG_SEG_SIZE (xlog_internal.h). The default wal_segment_size is not changed but I have increased the maximum size to 1GB.

Since  XLOG_SEG_SIZE is now variable, it could not be used directly in src/bin modules and few macros and few changes had to be made: 

  -  in guc.c , remove GUC_UNIT_XSEGS which used XLOG_SEG_SIZE and introduce show functions for the guc which used the unit (min_wal_size and max_wal_size).
  -  For pg_basebackup, add new replication command SHOW_WAL_SEGSZ to fetch the wal_segment_size in bytes. 

  - pg_controldata, pg_resetxlog, pg_rewind, fetch the xlog_seg_size from the ControlFile.

  - Since pg_xlogdump reads the wal files, it uses the file size to determine the xlog_seg_size.

  - In pg_test_fsync, a buffer of size XLOG_SEG_SIZE was created, filled with random data and written to a temporary file to check for any write/fsync error before performing the tests. Since it does not affect the actual performance results, the XLOG_SEG_SIZE in the module is replaced with the default value (16MB).

Please note that the documents are not updated in this patch. 

Feedback and suggestions are welcome.