Re: [REVIEW] Re: Compression of full-page-writes

On Fri, Feb 27, 2015 at 12:44 PM, Michael Paquier
 wrote:
> On Fri, Feb 27, 2015 at 8:01 AM, Michael Paquier
>  wrote:
>> On Fri, Feb 27, 2015 at 6:54 AM, Rahila Syed  wrote:
>>>>Even this patch doesn't work fine. The standby emit the following
>>>>error messages.
>>>
>>> Yes this bug remains unsolved. I am still working on resolving this.
>>>
>>> Following chunk IDs have been added in the attached patch as suggested
>>> upthread.
>>> +#define XLR_CHUNK_BLOCK_REFERENCE  0x10
>>> +#define XLR_CHUNK_BLOCK_HAS_IMAGE  0x04
>>> +#define XLR_CHUNK_BLOCK_HAS_DATA   0x08
>>>
>>> XLR_CHUNK_BLOCK_REFERENCE denotes chunk ID of block references.
>>> XLR_CHUNK_BLOCK_HAS_IMAGE is a replacement of BKPBLOCK_HAS_IMAGE
>>> and XLR_CHUNK_BLOCK_HAS DATA a replacement of BKPBLOCK_HAS_DATA.
>>
>> Before sending a new version, be sure that this get fixed by for
>> example building up a master with a standby replaying WAL, and running
>> make installcheck-world or similar. If the standby does not complain
>> at all, you have good chances to not have bugs. You could also build
>> with WAL_DEBUG to check record consistency.

+1

When I test the WAL or replication related features, I usually run
"make installcheck" and pgbench against the master at the same time
after setting up the replication environment.
typedef struct XLogRecordBlockHeader{
+    uint8        chunk_id;        /* xlog fragment id */    uint8        id;                /* block reference ID */

Seems this increases the header size of WAL record even if no backup block
image is included. Right? Isn't it better to add the flag info about backup
block image into XLogRecordBlockImageHeader rather than XLogRecordBlockHeader?
Originally we borrowed one or two bits from its existing fields to minimize
the header size, but we can just add new flag field if we prefer
the extensibility and readability of the code.

Regards,

-- 
Fujii Masao