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MySQL "file-per-table", database not selected Error

I have a small self- contained C# project with a MySQL database on a Win10 minicomputer. Although small and simple, a constant up-to-date backup of at least one table of the database is necessary. To add a replication server is not really feasible as the users want it totally easy to handle. So I thought a “file-per-table” on an outside directory (e.g. on a USB-stick on this minicomputer) could be the solution.
According to the MySQL 5.7 reference manual showing:
mysql> CREATE TABLE t1 (c1 INT PRIMARY KEY) DATA DIRECTORY = '/alternative/directory';
I tried this:
mysql> CREATE TABLE t1 (c1 INT PRIMARY KEY) DATA DIRECTORY = '/F/’;
I get:
ERROR 1046 (3D000): No database selected
May be there is a total misunderstanding when I think that I can create one table of my database on a USB-stick (drive “F”) to hold a duplicate of the important table inside the database.
And I thought that calling the database (mysql -u root -p
Enter password: *******) already selects this one database I mean. But of course I could have more databases under the same user and password….
So if I am not totally wrong, how do I have to select the database?
Thanks for taking a look at this.

It's confusing because some people use the word "database" to mean the instance of MySQL you log into. But others use the word "database" mean a schema, which is like a folder in which you can create tables. You cannot create a table unless you do it inside a schema.
In MySQL, the keywords DATABASE and SCHEMA are interchangeable.
You should review the MySQL tutorial, especially Creating and Using a Database.
That said, I think your plan to put a table on a USB stick drive is not going to work anyway. The file-per-table InnoDB tablespaces are not a backup. You can't just copy that file and get the data within it, and later restore the copy to another MySQL instance. The reason is that the file doesn't contain all the data. As you modify data, the changes go through different locations in RAM and in the central tablespace before they are eventually integrated into the file-per-table file. This can happen long after your application commits changes to MySQL. The changes are safe, they just aren't stored in the file-per-table file until some time later.
If you store a table on USB stick drive, and you yank it from the computer before it's fully in sync with recent changes, you will corrupt your database.
Another problem is that USB stick drives are many times slower than the computer's main hard disk. If you try to store part of the database on a USB stick drive, it will compromise the performance of your application. You won't like the result.
If you need to run backups frequently, you should use the backup tool provided, which is mysqldump. You can back up an InnoDB table without locking it if you use the right option:
mysqldump --single-transaction mydatabase mytable > mytable.sql
The --single-transaction ensures a consistent read of the table(s) without locking it (as long as the table uses the InnoDB engine). It does this by using a transaction.
Re your comment:
You can run mysqldump pretty frequently. But it's still be something you must run. There are various scheduler tools for every operating system (for example, Windows 10 has the Task Scheduler).
But if you have to account for hard drive failure, you need to have some separate storage. For example, you could put the output of the mysqldump onto a USB drive. Or you could upload the dump file to cloud storage.
I strongly recommend you do NOT configure any of your MySQL tablespaces to reside on removable storage. I wrote above that it will cause poor performance, and a high risk of corrupting your database. I don't know how to be any clearer that this is a BAD thing to do.

Storing large files / binary data in a mysql database: when is it ok?

Ok, I have searched about this and read a few points of view about storing binary data in a [MySQL] database. Generally I consider this a bad idea and try to avoid it, favouring traditional file transfers and just storing a reference to the file in a database.
However, I am working on a project which requires database synchronisation with a remote/cloud database, not just for files, but also for settings and other user content. For this, and other reasons, I felt this might be an appropriate situation for binary storage in a database.
I have written a general system for the database sync which works well using Reflection and XML. I have also (against my instincts) integrated the file storage in to this system. Again, it works well - I chop files in to 64Kb BLOBs and store them in a table, with a file_id reference (linked to a seperate table which contains meta data such as file name/size/mime type).
This enables me to send bits and pieces as and when a connection is available, and also allows me to limit each request size to keep things running smoothly.
So far I have not found any issues with this, and have successfully imported and transferred over 1gb of data in both directions (over about 10-15 files / 16000 rows), but I worry about its scalability - will it slow down once there is 20gb+ data in there, or can MySQL handle it provided my queries are well structured?
Another reason for my decision to store the data in the database was that I figured I could simply add another HDD/storage device to MySQL if space ran low, in the hope of efficient scaling/replication/etc.
I would very much appreciate any views or comments as to whether this is a good or bad approach, and have I missed any obvious problems I'm likely to see once used in a production environment?
edit: I forgot to mention, the file sizes could range from 1KB to ~1GB
[Rough] Conclusion
Firstly: thanks very much to those who contributed a considered answer. Choosing the accepted answer here has been quite difficult as each has something decent to offer.
In the end (despite my hopes), I have decided that a pure MySQL storage server is at best only an ok solution (I still can't help wondering why they bother including the BLOB types though).
As the alternative, I am torn between #Nick Coons file system approach and #tadman's suggestion of a hybrid using a light weight key/value database engine such as leveldb. Provided the practicalities of using leveldb in this project are not an issue, this is most likely the approach I will work towards.
I have accepted tadman's answer on this basis; his answer was also most applicable and useful to my situation.
That being said, and for those that are interested: I have enjoyed quite a lot of success using only MySQL so far. I have tested a table storing over 15gb of binary data without any noticable negative side effects from to inserting/retrieving data from large tables (with careful queries). However, I am certain this is still very inefficient and either of the alternative methods mentioned will be significantly better.

I have to wonder why you're even bothering with a database at all, when the layer you've added on top to chunk, store, retrieve and reassemble would work just as well on a well-defined filesystem structure. MySQL wants all of its data on a single volume, so it's not a case of adding another drive whenever you feel like it, and replication of large amounts of binary data is going to be cripplingly slow as the binary logs will end up duplicating the amount of data you need to store.
The simplest approach is often the best one. Storing this in the filesystem directly is probably the best way to do it. If you need to keep an index of what's stored where, maybe you'd use a database like MySQL, but there's many ways to accomplish this same task. The more low-tech, the better. For example, don't rule out SQLite because an embedded database performs very well under light read and write load, and has the advantage of being "just a file" when it comes to backing up and restoring.
That being said, what you're doing sounds suspiciously similar to LevelDB, so before you commit to your approach, you'd have to see how it's significantly different than a key-value document store of that variety.

Short Answer:
I'm not sure there's a hard-lined way to answer this. You mentioned files being from 1KB to 1GB.. I wouldn't store binary data in a DB if it's going to anywhere near 1KB, let along 1GB. I may store a few bytes of binary data in a DB if it's incidental, but any large amount of data, especially that doesn't need to be searched, should be stored in the filesystem:
When you store data in a DB, you're storing it on a filesystem anyway, you've just added another layer (the DB) to the mix. There's a cost to this layer, so there ought to be a benefit to make up the difference. If you're storing the data so that you can search based on it or join it to other data, then this makes sense. But file data, binary or not, is typically not used in that way.
Example Implementation:
There are better methods to distribute file data than to enter it into a DB, such as a distributed filesystems (check into GlusterFS, MooseFS, both of which will scale by simply adding additional hard drives, whereas MySQL will not).
Typically, I'll store file data in the filesystem using an SHA1 hash of the data as the name of the file. If the hash is 98a75af529f07b1ef7be7400f51344b9f07b1ef7, then I'll store it in this directory structure:
./98/a7/98a75af529f07b1ef7be7400f51344b9f07b1ef7
That is, a top-level directory made up of the first two characters, a second-level directory made up of the second two characters, and then finally the file with the name of the total string. In this way, I can literally have billions of files without having so many in a single directory that the system is too slow to function.
Then I create a DB table with these columns to hold the meta data:
file_id, an auto_increment field
created, a field with a default value of current_timestamp
prev_id, more on this below
hash, the SHA1 hash on the filesystem
name, a textual name of the file (such as the original name that the file would have taken on disk.
When I need a hierarchical directory structure, I would also create a directory table and add a dir_id to the list of columns above.
If I edit the file represented by ./98/a7/98a75af529f07b1ef7be7400f51344b9f07b1ef7, I don't actually change that file on disk, I create a new one (because the new file contents would be represented by a new SHA1 hash), and create a new entry in the files table where prev_id equals the file_id of the file I edited. In other words, I now have versioning.
If I need this to be available in a distributed fashion, I setup MySQL replication and then use GlusterFS to replicate he filesystem across multiple servers.

I think you will find a fair amount of debate on this as I did when I began looking into this. I tend to lean toward storing in the file system and maintaining a reference. However, that is not to say that there is never a time to store binary data in a database.
I would say that simply to keep things in sync is not a reason within itself to make an argument for storing binary data in a database. There certainly are ways to keep file systems in sync so that as a database is kept in sync so is the file system.
The bottom line is that there is a fair amount of debate on this topic and you have to go with what works for you. If what you have set up works. Use it. Do performance and load testing to make sure it works. If it doesn't hold up, change it.

SaaS application needs to export/backup data to individual customer sites

We have a cloud based SaaS application and many of our customers (school systems) require that a backup of their data be stored on-site for them.
All of our application data is stored in a single MS SQL database. At the very top of the "hierarchy" we have an "Organization". This organization represents a single customer in our system. Each organization has many child tables/objects/data. Each having FK relationships that ultimately end at "Organization".
We need a way to extract a SINGLE customer's data from the database and bundle it in some way so that it can be downloaded to the customers site. Preferably in a SQL Express, SQLite or an access database.
For example: Organization -> Skill Area -> Program -> Target -> Target Data are all tables in the system. Each one linking back to the parent by a FK. I need to get all the target data, targets, programs and skill areas per organization and export that data.
Does anyone have any suggestions about how to do this within SQL Server, a C# service, or a 3-rd party tool?
I need this solution to be easy to replicate for each customer who wants this feature "turned on"
Ideas?

I'm a big fan of using messaging to propagate data at the moment, so here's a message based solution that will allow external customers to keep a local, in sync copy of the data which you provide on the web.
The basic architecture would be an online, password secured and user specific list of changes which have occurred in the system.
At the server side this list would be appended to any time there was a change to an entity which is relevant to the specific customer.
At the client would run an application which checks the list of changes for any it hasn't yet received and then applies them to its local database (in the order they occurred).
There a a bunch of different ways of doing the list based component of the system but my gut feeling is that you would be best to use something like RSS to do this.
Below is a practical scenario of how this could work:
A new skill area is created for organisation "my org"
The skill is added to the central database and associated with the "my org" reccord
A SkillAreaExists event is also added at the same time to the "my org" RSS with JSON or XML data specifying the properties of the new skill area
A new program is added to the skill area that was just created
The program is added to the central database and associated with the skill area
A ProgramExists event is also added at the same time to the "my org" RSS with JSON or XML data specifying the properties of the new program
A SkillAreaHasProgram event is also added at the same time to the "my org" RSS with JSON or XML data specifying an identifier for the skill area and program
The client agent checks the RSS feed and sees the new messages and processes them in order
When the SkillAreaExists event is processed a new Skill area is added to the local DB
When the ProgramExists event is processed a new Program is added to the local DB
When the SkillAreaHasProgram event is processed the program is linked to the skill area
This approach has a whole bunch of benefits over traditional point in time replication.
Its online, a consumer of this can get realtime updates if required
Consistancy is maintained by order, at any point in time in the event stream if you stop receiving events you have a local DB which accuratly reflects the central DB as at some point in time.
Its diff based, you only need to recieve changes
Its auditable, you can see whats actually happened not just the current state.
Its easily recoverable, if there's a data consistency issue you can revert the entire DB by replaying the event stream.
It allows for multiple consumers, lots of individual copies of the clients info can exist and function autonomously.
We have had a great deal of success with these techniques for replicating data between sites especially when they are only sometimes online.

While there are some very interesting enterprise solutions that have been suggested, I think my approach would be to develop a plane old scheduled backup solution that simply exports the data for each organisation with a stored procedure or just a number of select statements.
Admittedly you'll have to keep this up to date as your database schema changes but if this is a production application I cant imagine that happens very drastically.
There are any number of technologies available to do this, be it SSIS, a custom windows service, or even something as rudimentary as a scheduled task that kicks off a stored procedure from the command line.
The format you choose to export to is entirely up to you and should probably be driven by how the backup is intended to be used. I might consider writing data to a number of CSV files and zipping the result such that it could be imported into other platforms should the need arise.
Other options might be to copy data across to a scratch database and then simply create a SQL backup of that database.
However you choose to go about it, I would encourage you to ensure that the process is well documented and has as much automated installation and setup as possible. Systems with loosely coupled dependencies such as common file locations or scheduled tasks are prone to getting tweaked and changed over time. Without those tweaks and changes being recorded you can create a system that works but can't be replicated. Soon no one wants to touch it and no one remembers exactly how it works. When it eventual needs changing, or worse it breaks, you have to start reverse engineering before you can fix it.
In a cloud based environment this is especially important because you want to be able to deploy as quickly as possible. If there is a lot of configuration that needs to be done you're likely to make mistakes or just be inconsistent. By creating a nuke-and-repave deployment you have a single point that you can change installation and configuration, safe in the knowledge that the change will be consistent across any deployment.

From what i understand, you have one large database for all the clients, you use relations which lead to the table organization to know which data for which client, and you want to backup the data based on client => organization.
To backup the data you can use one of the following methods:
As the comments from #Phil, and #Kris you can use SSIS for automated backup, check this link for structure backup, and check this link for how to Export a Query Result to a File using SSIS and instead of file do it to access or SQL Server database.
Build an application\service using C# to select the data and export it manually, need time but customization has no limits.

Have you looked at StreamInsight?
http://www.microsoft.com/sqlserver/en/us/solutions-technologies/business-intelligence/complex-event-processing.aspx

When I've had to deal with backups of relational data in the past (in MySQL which isn't super different in terms of capability from MSSQL that you're running) is to create a backup "package" file which is essentially a zip file with a different file extension so that windows won't let users open it.
If you really want to get fancy, encrypt the file after zipping it and change the extension. I presume you're using ASP for your SaaS and since I'm a PHP-geek, I can't help too much with the code side of things, but the way I've handled this before was for a script that would package an entire Joomla site and Database for migration to a new server.
//open the MySQL connection
$dbc = mysql_connect($cfg->host,$cfg->user,$cfg->password);
//select the database
mysql_select_db($cfg->db,$dbc);
output( 'Getting database tables
');
//get all the tables in the database
$tables = array();
$result = mysql_query('SHOW TABLES',$dbc);
while($row = mysql_fetch_row($result)) {
$tables[] = $row[0];
}
output( 'Found '.count($tables).' tables to be migrated.
Exporting tables:
');
$return = "";
//cycle through the tables and get their create statements and data
foreach($tables as $table) {
$result = mysql_query('SELECT * FROM '.$table);
$num_fields = mysql_num_fields($result);
$return.= 'DROP TABLE IF EXISTS '.$table.";\n";
$row2 = mysql_fetch_row(mysql_query('SHOW CREATE TABLE '.$table));
$return.= $row2[1].";\n";
while($row = mysql_fetch_row($result)) {
$return.= 'INSERT INTO '.$table.' VALUES(';
for($j=0; $j<$num_fields; $j++) {
$row[$j] = mysql_escape_string($row[$j]);
$row[$j] = ereg_replace("\n","\\n",$row[$j]);
if (!empty($row[$j])) {
$return.= "'".$row[$j]."'" ;
} else {
$return.= "NULL";
}
if ($j<($num_fields-1)) {
$return.= ',';
}
}
$return.= ");\n";
}
}
That's the relevant portion of the code in PHP that loops the database structure and stores the recreation script in $result which can then be output to a file.
In your case, you don't want to recreate the databases, but rather the data itself. You've compounded the issue slightly since you have a SaaS that is prone to possible data structure changes which you'll need to be able to account for. My suggestion would be this then:
Use a similar system to the above to dump the relevant data from the individual tables. I'm simply pulling all the data, but you could pull only the parts that pertain to the individual user by using JOIN statements and whatnot. Dump the contents of each table's insert/replace statements into a file named after the table. Create a file called manifest.xml or something of that sort and populate it with the current version of your SaaS application, name/information, unique ID, etc of the client exporting the data.
Package all those files into a ZIP file, change the extension to whatever you want, encrypt it if you desire, etc. Let them download that backup file and you're set.
In your import script, you will need to read the version number of the exported data and compare it to some algorithm that can handle remapping the data based on revisions you make later on. This way if you need to re-import one of their backups later, you can correctly handle transitioning the data from when they pulled the backup to the current structure of the data in that table now.
Hopefully that helps ;)

Because you keep all the data in just one database, it will always be difficult to export/backup data on customer basis.
Even if you implement such scenario now, you will end up with two different places you need to maintain/change/test every time you change the database schema (fixing bugs, adding new features, optimization, etc).
I would recommend you to partition the data, say, by using a database per organization. Then you change your application just once (mainly around building a connection string for the specified organization), and then you can safely export/backup each database separately in a way you want it.
It also gives you a lot of extra benefits "for free" such as scalability and the ability to dedicate resources on per-organization base (whether it is needed in the future).
Say, you have a set of small and low priority (from a business point of view) organizations, and a big and high priority one. So you will be able to keep a set of small low priority databases on one server, but dedicate another one for that specific important big one.
Or if your current DB server is overloaded (perhaps you have A LOT of data and A LOT of requests to the database), you can simply get another cheap server and move half of the load without any changes in your system...
You still need to write something in order to split the existing big database into several small ones, but you do it just once, and after it is done this "migration tool" can be thrown away so you don't need to support it anymore.

Have you tried SyncFramework?
Have a look at this article!
It explains how to sync filtered data between databases using Sync Framework.
You can sync to the customer's database or sync to your own empty db and then export it as a file.

Did you thought about using an ORM? (Object Relational Mapper)
I know, and use, LLBLGen Pro (so I can talk only about the feature of this specific ORM)
Anyway, with LLBLGen you can reverse-engineer the DB and create a hierarchy of class that map the tables and relations of your DB.
Now If all the data of a customer is reachable via relations, I can tell to my ORM framework to load a single costumers (1 row of a specific table) and then load all the related data in the related table.
If the data is not too complex, it should be possible.
If you have hundreds of self referenced tables or strange relations, it may be undoable, it depend upon your data.
If all the data of a single customer is, say, 10'000 rows in 100 tables, it will probably work.
If all the data of is 100'000 rows in 1000 tables it "may" work if you have some times, and a lot of memory.
If all the data is 10'000'000 you probably cant load it all at once, and you'll need a more efficient way.
Anyway, if you can load all the data at once, then you'll have a nice "in memory" graph with all the data of a single customer, and then you can serialize this data, or project it on a dataset (obtaining a set of datatable/relations) and then serialize the dataset.
Using an ORM to load and export all the data of a single customer as explained, probably, is not the most efficient way of doing things, but when doable it's a simple and cheap way.
Naturally, with or without ORM, you can find hundreds of different way to export this data :-)

For you design, you should have sharded your database for customers.
However, as you have already developed the database design, I suggest you to create a temp database and create the new tables in this temp database using the FK relation.
For this, you need to sort the tables based on the FK relationship and create them in the temp database.
Then, select the table data from the source database and insert them in the temp database.
You can also use this technique to shard your database and revamp your database design.
Aravind

Multiple MDF FIles VS Single DataBase(SQL Server)

I'm working on a web2 project that i would like has thousands of rows per day by users.
for handling this size of data i designed database like this:
one .mdf and .ldf file as Minor DataBase and 1 Major DB to save and query the User Accounts and DataBase Files addresses.
i have worked several months for this plan and now i can manage it easily.
i want to know if it is good idea to handle huge size of Independent datas ?
witch has better performance in your opinion ? opening connection of many small .mdf files or just a huge dataBase.
afterwards i'll divide the mdf Repository in several computers.
all of them are handled by C# and linq (.net4)
// Later Descriptions
i built this plan and it works fine.
for example: opening every small mdf file takes 1sec time and query it in 0.0sec. it makes static time for every connection but in single Database for 50rows system must find them in for instance 200,000 rows and takes about 4-5sec in my system with simple select query with Primary key.
for other instance i want to get a row between 500,000 rows to bind page content and select 50 Comments between 2milmions row, and get count of votes of every comment, view count in day, week, month and total. count of likes, answer of comments and get more datas from 2-3 other tables, this querys are heavy and take more time than small slave database.
i think a good design and processes must work easy for system.
the only problem is that small slave databases with sql server files takes more physical size about 3MB per DataBase.

There is no reason to split something that could/should exist as a single database in to multiple independent parts.
There are already mechanisms to partition a single logical database across multiple files: Files and Filegroups Architecture as well as to partition large tables (A few thousand rows per day doesn't really qualify as a large table).

"Thousands of rows per day" should be pocket change for Sql Server.
First, I voted up Alex K answer. File groups will get you to where you want to be most likely. Partitioned tables may be overkill, and is only available in Enterprise version and is not for the light hearted.
What I will add is:
http://www.google.com/#q=glenn+berry+dmv&bav=on.2,or.r_gc.r_pw.&fp=73d2ceaabb6b01bf&hl=en
You need to tweak your indexes. In the good vs. better vs. best category, Glenn Berry's DMV queries are "better". Those queries will help you fix the majority of issues.
In the "best" category is pain staking looking at each stored procedure, and looking at the execution plan and trying out different things. This is what a good dba is able to provide.
Here are some "basics" on file setup considerations. Pay attention the TEMP database setup.
http://technet.microsoft.com/en-us/library/cc966534.aspx

its difficult to manage small MDF file u have to go with SQL server and SQL server database provide 10GB data storage per one database os its easy

C# and Access 2000

I have developed an network application that is in use in my company for last few years.
At start it was managing information about users, rights etc.
Over the time it grew with other functionality. It grew to the point that I have tables with, let's say 10-20 columns and even 20,000 - 40,000 records.
I keep hearing that Access in not good for multi-user environments.
Second thing is the fact that when I try to read some records from the table over the network, the whole table has to be pulled to the client.
It happens because there is no database engine on the server side and data filtering is done on the client side.
I would migrate this project to the SQL Server but unfortunately it cannot be done in this case.
I was wondering if there is more reliable solution for me than using Access Database and still stay with a single-file database system.
We have quite huge system using dBase IV.
As far as I know it is fully multiuser database system.
Maybe it will be good to use it instead of Access?
What makes me not sure is the fact that dBase IV is much older than Access 2000.
I am not sure if it would be a good solution.
Maybe there are some other options?

If you're having problems with your Jet/ACE back end with the number of records you mentioned, it sounds like you have schema design problems or an inefficiently-structured application.
As I said in my comment to your original question, Jet does not retrieve full tables. This is a myth propagated by people who don't have a clue what they are talking about. If you have appropriate indexes, only the index pages will be requested from the file server (and then, only those pages needed to satisfy your criteria), and then the only data pages retrieved will be those that have the records that match the criteria in your request.
So, you should look at your indexing if you're seeing full table scans.
You don't mention your user population. If it's over 25 or so, you probably would benefit from upsizing your back end, especially if you're already comfortable with SQL Server.
But the problem you described for such tiny tables indicates a design error somewhere, either in your schema or in your application.
FWIW, I've had Access apps with Jet back ends with 100s of thousands of records in multiple tables, used by a dozen simultaneous users adding and updating records, and response time retrieving individual records and small data sets was nearly instantaneous (except for a few complex operations like checking newly entered records for duplication against existing data -- that's slower because it uses lots of LIKE comparisons and evaluation of expressions for comparison). What you're experiencing, while not an Access front end, is not commensurate with my long experience with Jet databases of all sizes.

You may wish to read this informative thread about Access: Is MS Access (JET) suitable for multiuser access?

For the record this answer is copied/edited from another question I answered.
Aristo,
You CAN use Access as your centralized data store.
It is simply NOT TRUE that access will choke in multi-user scenarios--at least up to 15-20 users.
It IS true that you need a good backup strategy with the Access data file. But last I checked you need a good backup strategy with SQL Server, too. (With the very important caveat that SQL Server can do "hot" backups but not Access.)
So...you CAN use access as your data store. Then if you can get beyond the company politics controlling your network, perhaps then you could begin moving toward upfitting your current application to use SQL Server.
I recently answered another question on how to split your database into two files. Here is the link.
Creating the Front End MDE
Splitting your database file into front end : back end is sort of a key to making it more performant. (Assume, as David Fenton mentioned, that you have a reasonably good design.)
If I may mention one last thing...it is ridiculous that your company won't give you other deployment options. Surely there is someone there with some power who you can get to "imagine life without your application." I am just wondering if you have more power than you might realize.
Seth

The problems you experience with an Access Database shared amongst your users will be the same with any file based database.
A read will pull a lot of data into memory and writes are guarded with some type of file lock. Under your environment it sounds like you are going to have to make the best of what you have.

"Second thing is the fact that when I try to read some records from the table over the network, the whole table has to be pulled to the client. "
Actually no. This is a common misstatement spread by folks who do not understand the nature of how Jet, the database engine inside Access, works. Pulling down all the records, or excessive number of records, happens because you don't have all the fields used in the selection criteria or sorting in the index. We've also found that indexing yes/no aka boolean fields can also make a huge difference in some queries.
What really happens is that Jet brings down the index pages and data pages which are required. While this is a lot more data than a database engine would create this is not the entire table.
I also have clients with 600K and 800K records in various tables and performance is just fine.

We have an Access database application that is used pretty heavily. I have had 23 users on all at the same time before without any issues. As long as they don't access the same record then I don't have any problems.
I do have a couple of forms that are used and updated by several different departments. For instance I have a Quoting form that contains 13 different tabs and 10-20 fields on each tab. Users are typically in a single record for minutes editing and looking for information. To avoid any write conflicts I call the below function any time a field is changed. As long as it is not a new record being entered, then it updates.
Function funSaveTheRecord()
If ([chkNewRecord].value = False And Me.Dirty) Then
'To save the record, turn off the form's Dirty property
Me.Dirty = False
End If
End Function
They way I have everything setup is as follows:
PDC.mdb <-- Front End, Stored on the users machine. Every user has their own copy. Links to tables found in PDC_be.mdb. Contains all forms, reports, queries, macros, and modules. I created a form that I can use to toggle on/off the shift key bipass. Only I have access to it.
PDC_be.mdb <-- Back End, stored on the server. Contains all data. Only form and VBA it contains is to toggle on/off the shift key bipass. Only I have access to it.
Secured.mdw <-- Security file, stored on the server.
Then I put a shortcut on the users desktop that ties the security file to the front end and also provides their login credentials.
This database has been running without error or corruption for over 6 years.

Access is not a flat file database system! It's a relational database system.

You can't use SQL Server Express?
Otherwise, MySQL is a good database.
But if you can't install ANYTHING (you should get into those politics sooner rather than later -- or it WILL be later), just use you existing database system.
Basically with Access, it cannot handle more than 5 people connected at the same time, or it will corrupt on you.