Request a Demo
Home   >   mailing lists

Re: A bug when use get_bit() function for a long bytea string - Mailing list pgsql-hackers

From movead.li@highgo.ca
Subject Re: A bug when use get_bit() function for a long bytea string
Date
Msg-id 2020032817093521193529@highgo.ca
Whole thread
In response to A bug when use get_bit() function for a long bytea string  ("movead.li@highgo.ca" <movead.li@highgo.ca>)
Responses Re: A bug when use get_bit() function for a long bytea string
List pgsql-hackers
Tree view
I want to resent the mail, because last one is in wrong format and hardly to read.

In addition, I think 'Size' or 'size_t' is rely on platform, they may can't work on 32bit
system. So I choose 'int64' after ashutosh's review.

>>I think the second argument indicates the bit position, which would be max bytea length * 8. If max bytea length covers whole int32, the second argument >needs to be wider i.e. int64.
>Yes, it makes sence and followed.

>>I think we need a similar change in byteaGetBit() and byteaSetBit() as well.
Sorry, I think it's my mistake, it is the two functions above should be changed.


>>Some more comments on the patch
>> struct pg_encoding
>> {
>>- unsigned (*encode_len) (const char *data, unsigned dlen);
>>+ int64 (*encode_len) (const char *data, unsigned dlen);
>>  unsigned (*decode_len) (const char *data, unsigned dlen);
>>  unsigned (*encode) (const char *data, unsigned dlen, char *res);
>>  unsigned (*decode) (const char *data, unsigned dlen, char *res);
>> Why not use return type of int64 for rest of the functions here as well?
>>  res = enc->encode(VARDATA_ANY(data), datalen, VARDATA(result));
>>  /* Make this FATAL 'cause we've trodden on memory ... */
>>- if (res > resultlen)
>>+ if ((int64)res > resultlen)
>>
>>if we change return type of all those functions to int64, we won't need this cast.
>I change the 'encode' function, it needs an int64 return type, but keep other 
>functions in 'pg_encoding', because I think it of no necessary reason.

>>Ok, let's leave it for a committer to decide. 
Well, I change all of them this time, because Tom Lane supports on next mail.

 
>Some more review comments.
>+   int64       res,resultlen;
>We need those on separate lines, possibly.
Done

>+   byteNo = (int32)(n / BITS_PER_BYTE);
>Does it hurt to have byteNo as int64 so as to avoid a cast. Otherwise, please
>add a comment explaining the reason for the cast. The comment applies at other
>places where this change appears.
>-       int         len;
>+       int64       len;
>Why do we need this change?
>        int         i;
It is my mistake as describe above, it should not be 'bitgetbit()/bitsetbit()'  to be changed.



>>It might help to add a test where we could pass the second argument something
>>greater than 1G. But it may be difficult to write such a test case.
>Add two test cases.
 
>+
>+select get_bit(
>+        set_bit((repeat('Postgres', 512 * 1024 * 1024 / 8))::bytea, 1024 * 1024 * 1024 + 1, 0)
>+       ,1024 * 1024 * 1024 + 1);

>This bit position is still within int4.
>postgres=# select pg_column_size(1024 * 1024 * 1024 + 1); 
> pg_column_size
>----------------
>              4   
>(1 row)

>You want something like
>postgres=# select pg_column_size(512::bigint * 1024 * 1024 * 8); 
> pg_column_size
>----------------
>              8   
>(1 row)
I intend to test size large then 1G, and now I think you give a better idea and followed.



Highgo Software (Canada/China/Pakistan)
URL : www.highgo.ca
EMAIL: mailto:movead(dot)li(at)highgo(dot)ca

pgsql-hackers by date:

Previous
From: i.taranov@postgrespro.ru
Date:
Subject: [PATCH] postgresql.conf.sample->postgresql.conf.sample.in
Next
From: David Rowley
Date:
Subject: Re: Berserk Autovacuum (let's save next Mandrill)