On Thu, Mar 5, 2015 at 9:14 PM, Syed, Rahila <rahila.s...@nttdata.com> wrote:
> Please find attached  a patch. As discussed, flag to denote compression and 
> presence of hole in block image has been added in XLogRecordImageHeader 
> rather than block header.
> Following are WAL numbers based on attached  test script  posted by Michael 
> earlier in the thread.
>                                                       WAL generated
> FPW compression on           122.032 MB
> FPW compression off           155.223 MB
> HEAD                                          155.236 MB
> Compression : 21 %
> Number of block images generated in WAL :   63637

ISTM that we are getting a nice thing here. I tested the patch and WAL
replay is working correctly.

Some nitpicky comments...

+ * bkp_info stores flags for information about the backup block image
+ * BKPIMAGE_IS_COMPRESSED is used to identify if a given block image
is compressed.
+ * BKPIMAGE_WITH_HOLE is used to identify the presence of a hole in a
block image.
+ * If the block image has no hole, it is ensured that the raw size of
a compressed
+ * block image is equal to BLCKSZ, hence the contents of
+ * XLogRecordBlockImageCompressionInfo are not necessary.
Take care of the limit of 80 characters per line. (Perhaps you could
run pgindent on your code before sending a patch?). The first line of
this paragraph is a sentence in itself, no?

In xlogreader.c, blk->with_hole is a boolean, you could remove the ==0
and ==1 it is compared with.

+      /*
+       * Length of a block image must be less than BLCKSZ
+       * if the block has hole
+       */
"if the block has a hole." (End of the sentence needs a dot.)

+       /*
+        * Length of a block image must be equal to BLCKSZ
+        * if the block does not have hole
+        */
"if the block does not have a hole."


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