Fatal error: Allowed memory size exhausted

Most of the time “Allowed memory size…” is about low memory.
Try to changedefine( 'WP_MAX_MEMORY_LIMIT' , '512M' );

Exhausted memory is often because of an infinite loop in your code.
Try to deactivating all plugins, and try switching to the Twenty Seventeen theme to rule-out a theme-specific issue (theme functions can interfere like plugins).

Clone a website to local dev environment – to be sure its not some hosting thing (memory limit, or other limit)

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• This reply was modified 7 years ago by Jan Dembowski.

Thanks for super fast response.
Yes increase of memory limit solved the issue. In DB I can see that the query takes more than 5s.
Query_time: 5.497520 Lock_time: 0.484138 Rows_sent: 841 Rows_examined: 47158
It is option table.
postmeta is even larger: 433 541 rows

I think my woocommerce get fat ??

Thanks, have a good luck
Michal

Thank you for reporting back @osimiso, glad you resolved the problem.

Maybe this can help:
Reduce the number of revisions that are saved (every time you edit post, product, page revision is saved)
define( 'WP_POST_REVISIONS', 2 );
Revisions WordPress Codex

BACKUP website

Optimize with WP-Optimize plugin:
WP-Optimize WordPress plugin

Cleaning:
Delete all security logs (iThemes Security, WordFence…),
Delete unused Products, Posts, also clear/reset Server logs (CPanel or ask Host to do it)
Delete old orders (that you dont need, PDF slips etc..)

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• This reply was modified 7 years, 2 months ago by DecomTeam.
• This reply was modified 7 years ago by Jan Dembowski.

This wordpress memory exhausted error could be solved by increasing php memory by editing the wp-config.php file and adding this line:
define( ‘WP_MEMORY_LIMIT’, ‘256M’ );
If it is not working, you might need to contact your hosting provider for that.

source: https://www.webxen.com/kb/wordpress-fatal-error-allowed-memory-size-of-67108864-bytes-exhausted/