MySQL – Fix OOM Errors in Boolean Fulltext Search Queries

I am experiencing intermittent oom errors when running queries that have a boolean fulltext search in them.

I am on AWS Aurora (t2.medium).

Here is an example query, considering the table "sets" which has a fulltext index on the columns (savename, title) and has about 2 million rows in it.

        select          sets.id, sets.title,
                        drafts.draftId as draftId,
                        folderSets.folderId as folderId,
                        concat_ws(' ', savedBy.firstname, savedBy.lastname) as savedBy,
                        match(sets.savename, sets.title) against ("+s*" in boolean mode) as relevance
        from            sets as sets
        join            folderSets as folderSets on folderSets.setId = sets.id
        join            folders as folders on folders.id = folderSets.folderId 
        left join       draftSets as drafts on drafts.originalId = sets.id and drafts.userId = ?
        left join       users as savedBy on savedBy.id = folderSets.userId
        where           (folders.userId = ?)
                        and match(sets.savename, sets.title) against ("+s*" in boolean mode)
        order by        relevance
        limit           0, 25;

This query takes about 5 seconds to run. If I hammer it a few times, the query is likely to fail with an OOM.

If I change the boolean fulltext search phrase from "+s*" to "+sam*" — so there are more characters before the wildcard — the same query executies in about .15 seconds, without any issues.

If I remove the boolean search altogehter from the query, the query runs even faster, without any issues.

So it seems like there is something going on with the boolean fulltext portion of the query that is hitting a mysql limit.

Here are the innodb fulltext system variables:

ft_boolean_syntax................... + -><()~*:""&|
ft_max_word_len..................... 84
ft_min_word_len..................... 1
ft_query_expansion_limit............ 20
ft_stopword_file.................... /dev/null
innodb_ft_aux_table................. 
innodb_ft_cache_size................ 8000000
innodb_ft_enable_diag_print......... OFF
innodb_ft_enable_stopword........... OFF
innodb_ft_max_token_size............ 84
innodb_ft_min_token_size............ 1
innodb_ft_num_word_optimize......... 2000
innodb_ft_result_cache_limit........ 2000000000
innodb_ft_server_stopword_table..... 
innodb_ft_sort_pll_degree........... 2
innodb_ft_total_cache_size.......... 640000000
innodb_ft_user_stopword_table.......

Does anyone have any advice on any tuning that can be done to reduce the likelihood of an OOM related to boolean fulltext? I am unclear is this is something that can / should be fixed at the sql query level / the mysql innodb settings level / or if I am in the situation of needing to increase the size of the aws rds instance.

Thanks (in advance) for your help!