Best practice: Import mySQL file in PHP; split queries

Question

I have a situation where I have to update a web site on a shared hosting provider. The site has a CMS. Uploading the CMS\'s files is pretty straightforward using FTP.

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Answer 1

Export

The first step is getting the input in a sane format for parsing when you export it. From your question it appears that you have control over the exporting of this data, but not the importing.

~: mysqldump test --opt --skip-extended-insert | grep -v '^--' | grep . > test.sql

This dumps the test database excluding all comment lines and blank lines into test.sql. It also disables extended inserts, meaning there is one INSERT statement per line. This will help limit the memory usage during the import, but at a cost of import speed.

Import

The import script is as simple as this:

 1MB (1000000)
        // which is unlikely given the size of your DB
        // Note that it has a DIRECT effect on your scripts memory
        // usage.
        $buffer = stream_get_line($handle, 1000000, ";\n");
        $mysqli->query($buffer);
    }
}
echo "Peak MB: ",memory_get_peak_usage(true)/1024/1024;

This will utilize an absurdly low amount of memory as shown below:

daves-macbookpro:~ hobodave$ du -hs test.sql 
 15M    test.sql
daves-macbookpro:~ hobodave$ time php import.php 
Peak MB: 1.75
real    2m55.619s
user    0m4.998s
sys 0m4.588s

What that says is you processed a 15MB mysqldump with a peak RAM usage of 1.75 MB in just under 3 minutes.

Alternate Export

If you have a high enough memory_limit and this is too slow, you can try this using the following export:

~: mysqldump test --opt | grep -v '^--' | grep . > test.sql

This will allow extended inserts, which insert multiple rows in a single query. Here are the statistics for the same datbase:

daves-macbookpro:~ hobodave$ du -hs test.sql 
 11M    test.sql
daves-macbookpro:~ hobodave$ time php import.php 
Peak MB: 3.75
real    0m23.878s
user    0m0.110s
sys 0m0.101s

Notice that it uses over 2x the RAM at 3.75 MB, but takes about 1/6th as long. I suggest trying both methods and seeing which suits your needs.

Edit:

I was unable to get a newline to appear literally in any mysqldump output using any of CHAR, VARCHAR, BINARY, VARBINARY, and BLOB field types. If you do have BLOB/BINARY fields though then please use the following just in case:

~: mysqldump5 test --hex-blob --opt | grep -v '^--' | grep . > test.sql