ServerSide50KPagination.cls

public class ServerSide50KPagination {
    Id[] recordIds;
    public Integer maxPage { get; set; }
    public Integer pageNumber { get; set; }
    public Integer pageSize { get; set; }
    public Account[] records { get; set; }

    public ServerSide50KPagination() {
        recordIds = new Id[0];
        for(Account record: [SELECT Id FROM Account ORDER BY Name]) {
            recordIds.add(record.Id);
        }
        pageSize = 10;
        maxPage = (recordIds.size()+(pageSize-1)) / pageSize;
    }
    
    public void firstPage() {
        pageNumber = 1;
        loadPage();
    }
    public void previousPage() {
        pageNumber = Math.max(1, pageNumber - 1);
        loadPage();
    }
    public void nextPage() {
        pageNumber = Math.min(maxPage, pageNumber + 1);
        loadPage();
    }
    public void lastPage() {
        pageNumber = maxPage;
        loadPage();
    }
    public void loadPage() {
        Id[] currentPage = new Id[0];
        records = new Account[0];
        for(Integer index = (pageNumber-1)*pageSize, 
                size = Math.min(pageNumber*pageSize, recordIds.size());
                index < size; index++) {
            currentPage.add(recordIds[index]);
        }
        Map<Id, Account> accounts = new Map<Id, Account>(
            [SELECT Name, Industry FROM Account WHERE Id = :currentPage]
        );
        for(Id recordId: currentPage) {
            records.add(accounts.get(recordId));
        }
    }
    public void changePageSize() {
        maxPage = (recordIds.size()+(pageSize-1)) / pageSize;
        firstPage();
    }
    public void refreshView() {
        loadPage();
    }
}

ServerSide50KPagination.page

<apex:page controller="ServerSide50KPagination">
    <apex:form id="form">
        <apex:actionStatus id="status" startText="Working..." />
    	<apex:pageBlock rendered="{!pageNumber!=null}">
            <apex:pageBlockButtons>
            	<apex:commandButton status="status" reRender="form" action="{!firstPage}" value="First"/>
            	<apex:commandButton status="status" reRender="form" action="{!previousPage}" value="Previous"/>
                {!pageNumber} / {!maxPage}
            	<apex:commandButton status="status" reRender="form" action="{!nextPage}" value="Next"/>
            	<apex:commandButton status="status" reRender="form" action="{!lastPage}" value="Last"/>
                Page Size:
                <apex:selectList value="{!pageSize}" size="1" multiselect="false">
                    <apex:selectOption itemValue="10" itemLabel="10" />
                    <apex:selectOption itemValue="25" itemLabel="25" />
                    <apex:selectOption itemValue="50" itemLabel="50" />
                    <apex:selectOption itemValue="100" itemLabel="100" />
                    <apex:actionSupport status="status" action="{!changePageSize}" reRender="form" event="onchange" />
                </apex:selectList>
            </apex:pageBlockButtons>
            <apex:pageBlockTable value="{!records}" var="acct">
                <apex:column value="{!acct.Name}" />
                <apex:column value="{!acct.Industry}" />
            </apex:pageBlockTable>
        </apex:pageBlock>
        <apex:actionFunction status="status" name="refreshPage" action="{!firstPage}" rendered="{!pageNumber=null}" reRender="form"/>
    </apex:form>
        <script>
        if(refreshPage) {
            refreshPage();
        }
        </script>
</apex:page>